chore: Fix package build scripts for git-deps and npm-link symlinks (#746)

## Background
This PR is copied from #481. It was contributed by @jasonkarns a couple of years ago. I just pulled his changes, merged master and resolved conflicts.

## Summary
Main change: `prepublishOnly` is the wrong lifecycle script for building/compiling. prepublishOnly does not run during install for git-deps; nor does it run when a package is being symlinked via npm-link. The correct script is `prepare`.

This PR:
- ensures the build/bundle/compile script is accurately defined as `build` so as to be run properly by the top level `lerna run build` script.
- ensures "clean" is run before building
- ensures `clean` is defined and exposed such that `lerna run clean` works properly
- ensures `build` is invoked during `prepare` lifecycle hook (packing, publishing, git-installing, npm-linking)
- preserves `npm test` being run during `prepublishOnly`
- adds package tarball pattern to gitignore so npm-pack can be run for inspection
- removes unnecessary files from `package.json#files` array (license, changelog, readme, and package.json files are included automatically)
- renames CHANGELOG.MD to be cased properly

## Test plan
No code changes

Author: zashraf1985

.gitignore

@@ -1,9 +1,12 @@
-.DS_STORE
+node_modules/
+/packages/*/optimizely-*.tgz
+
 npm-debug.log
-dist
-node_modules
 lerna-debug.log
 
 coverage/
+dist/
 
+# user-specific ignores ought to be defined in user's `core.excludesfile`
 .idea/*
+.DS_STORE

packages/datafile-manager/package.json

@@ -20,11 +20,7 @@
     "test": "__test__"
   },
   "files": [
-    "lib",
-    "LICENSE",
-    "CHANGELOG",
-    "README.md",
-    "package.json"
+    "lib"
   ],
   "publishConfig": {
     "access": "public"
@@ -61,10 +57,13 @@
     }
   },
   "scripts": {
+    "clean": "rm -rf lib",
     "lint": "tsc --noEmit && eslint --fix 'src/**/*.ts' '__test__/**/*.ts'",
     "test": "jest",
     "posttest": "npm run lint",
-    "tsc": "rm -rf lib && tsc",
-    "prepublishOnly": "npm run lint && npm test && npm run tsc"
+    "prebuild": "npm run clean",
+    "build": "tsc",
+    "prepare": "npm run build",
+    "prepublishOnly": "npm test"
   }
 }

packages/event-processor/CHANGELOG.MD renamed to packages/event-processor/CHANGELOG.md

@@ -13,16 +13,15 @@
     "test": "test"
   },
   "files": [
-    "lib",
-    "LICENSE",
-    "CHANGELOG",
-    "README.md",
-    "package.json"
+    "lib"
   ],
   "scripts": {
-    "tsc": "rm -rf lib && tsc",
+    "clean": "rm -rf lib",
+    "prebuild": "npm run clean",
+    "build": "tsc",
     "test": "jest",
-    "prepublishOnly": "jest && npm run tsc"
+    "prepare": "npm run build",
+    "prepublishOnly": "npm test"
   },
   "repository": {
     "type": "git",

packages/event-processor/package.json

@@ -12,16 +12,15 @@
     "test": "test"
   },
   "files": [
-    "lib",
-    "LICENSE",
-    "CHANGELOG",
-    "README.md",
-    "package.json"
+    "lib"
   ],
   "scripts": {
-    "tsc": "rm -rf lib && tsc",
+    "clean": "rm -rf lib",
+    "prebuild": "npm run clean",
+    "build": "tsc",
     "test": "jest",
-    "prepublishOnly": "jest && npm run tsc"
+    "prepare": "npm run build",
+    "prepublishOnly": "npm test"
   },
   "repository": {
     "type": "git",

packages/logging/CHANGELOG.MD renamed to packages/logging/CHANGELOG.md

@@ -23,7 +23,8 @@
     "cover": "nyc report -r lcov",
     "precoveralls": "npm run cover",
     "coveralls": "< coverage/lcov.info coveralls",
-    "prepublishOnly": "npm run build && npm test && npm run test-xbrowser && npm run test-umdbrowser"
+    "prepare": "npm run build",
+    "prepublishOnly": "npm test && npm run test-ci"
   },
   "repository": {
     "type": "git",
@@ -87,11 +88,7 @@
   },
   "files": [
     "dist/",
-    "lib/",
-    "LICENSE",
-    "CHANGELOG",
-    "README.md",
-    "package.json"
+    "lib/"
   ],
   "nyc": {
     "temp-dir": "coverage/raw"

packages/logging/package.json

@@ -12,16 +12,15 @@
     "test": "test"
   },
   "files": [
-    "lib",
-    "LICENSE",
-    "CHANGELOG",
-    "README.md",
-    "package.json"
+    "lib"
   ],
   "scripts": {
-    "tsc": "rm -rf lib && tsc",
+    "clean": "rm -rf lib",
+    "prebuild": "npm run clean",
+    "build": "tsc",
     "test": "jest",
-    "prepublishOnly": "jest && npm run tsc"
+    "prepare": "npm run build",
+    "prepublishOnly": "npm test"
   },
   "repository": {
     "type": "git",