Global and local .gitconfig get and set functions

[jettseale]

Includes two main functions:

1. getConfig returns the value of the given corresponding key path from a specified local .gitconfig file. If this fails, it searches for the value in the global .gitconfig file. If this fails, it returns undefined.
2. setConfig changes the value of the given corresponding key path. Depending on the which parameter, it either writes to the local .gitconfig file, the global .gitconfig file, or both. If the given value is undefined, it deletes the entry.

Also includes three helper functions for the above two functions:

1. findAllByKey recursively finds all values within a given nested object that correspond to a given key.
2. getGlobalGitAuthorInfo finds the global .gitconfig file path, then asynchronously constructs a parseGitConfig.Config object containing all of the fields found within the global .gitconfig file.
3. replaceObjKey replaces a given parseGitConfig.Config object key value with another given value.

[nelsonni]

These changes are almost ready for merging. Once the requested changes have been made and pushed up, I will approve and integrate them. However, please be aware that the CI jobs failed due to some tests and snapshots needing to be updated: https://github.com/EPICLab/synectic/pull/230/checks?check_run_id=1495905949. I'll still approve the changes regardless, but if you can update the snapshots that would be helpful.

[nelsonni]

These changes are almost ready for merging. Once the requested changes have been made and pushed up, I will approve and integrate them. However, please be aware that the CI jobs failed due to some tests and snapshots needing to be updated: https://github.com/EPICLab/synectic/pull/230/checks?check_run_id=1495905949. I'll still approve the changes regardless, but if you can update the snapshots that would be helpful.

Actually, never mind about the CI test results. Apparently timestamps in Ubuntu don't default to include timezone modifiers and instead use the -00:00 timezone:

    - Snapshot  - 2
    + Received  + 2

      Object {
        "40d14391c": Object {
          "captured": false,
    -     "created": "2019-11-19T19:22:47.572-08:00",
    +     "created": "2019-11-20T03:22:47.572-00:00",
          "id": "40d14391c",
          "left": 178,
          "metafile": "29334943",
    -     "modified": "2019-11-22T12:54:11.374-08:00",
    +     "modified": "2019-11-22T20:54:11.374-00:00",
          "name": "card1",
          "top": 540,
          "type": "Editor",
        },
      }

Tests will have to be fixed by me in another PR.