Edit file workflow for creating a fork and proposing changes

When viewing a file that the user can't edit because they can't write to
the branch, the edit button is no longer disabled.

If no user fork of the repository exists, there is now a page create one.
It will automatically create a fork with a single branch matching the one
being viewed, and a unique repository name will be automatically picked.

If the fork exists, an message will explain at the top of the edit page
explaining that the changes will be applied to a branch in the fork. The
base repository branch will be pushed to a new branch to the fork, and
then the edits will be applied on top.

This all happens when accessing /_edit/, so that for example online
documentation can have an "edit this page" link to the base repository
that does the right thing.

Author: brechtvl

options/locale/locale_en-US.ini

@@ -1334,7 +1334,6 @@ editor.cannot_edit_non_text_files = Binary files cannot be edited in the web int
 editor.edit_this_file = Edit File
 editor.this_file_locked = File is locked
 editor.must_be_on_a_branch = You must be on a branch to make or propose changes to this file.
-editor.fork_before_edit = You must fork this repository to make or propose changes to this file.
 editor.delete_this_file = Delete File
 editor.must_have_write_access = You must have write access to make or propose changes to this file.
 editor.file_delete_success = File "%s" has been deleted.
@@ -1394,6 +1393,16 @@ editor.user_no_push_to_branch = User cannot push to branch
 editor.require_signed_commit = Branch requires a signed commit
 editor.cherry_pick = Cherry-pick %s onto:
 editor.revert = Revert %s onto:
+editor.fork_create = Fork Repository to Propose Changes
+editor.fork_create_description = You can not edit this repository directly. Instead you can create a fork, make edits and create a pull request.
+editor.fork_edit_description = You can not edit this repository directly. The changes will be written to your fork <b>%s</b>, so you can create a pull request.
+editor.fork_failed_to_push_branch = Failed to push branch %s to your repoitory.
+editor.cannot_find_editable_repo = Can not find repository to apply the edit to. Was it deleted while editing?
+editor.fork_not_editable = Fork Repository Not Editable
+editor.fork_internal_error = Internal error loading repository information about <b>%s</b>.
+editor.fork_is_archived = Your repository <b>%s</b> is archived. Unarchive it in repository settings to make changes.
+editor.fork_code_disabled = Code is disabled in your repository <b>%s</b>. Enable code in repository settings to make changes.
+editor.fork_no_permission = You do not have permission to write to repository <b>%s</b>.
 
 commits.desc = Browse source code change history.
 commits.commits = Commits

routers/web/repo/cherry_pick.go

@@ -47,15 +47,15 @@ func CherryPick(ctx *context.Context) {
 		ctx.Data["commit_message"] = splits[1]
 	}
 
-	canCommit := renderCommitRights(ctx)
+	canCommit := renderCommitRights(ctx, ctx.Repo.Repository)
 	ctx.Data["TreePath"] = ""
 
 	if canCommit {
 		ctx.Data["commit_choice"] = frmCommitChoiceDirect
 	} else {
 		ctx.Data["commit_choice"] = frmCommitChoiceNewBranch
 	}
-	ctx.Data["new_branch_name"] = GetUniquePatchBranchName(ctx)
+	ctx.Data["new_branch_name"] = GetUniquePatchBranchName(ctx, ctx.Repo.Repository)
 	ctx.Data["last_commit"] = ctx.Repo.CommitID
 	ctx.Data["LineWrapExtensions"] = strings.Join(setting.Repository.Editor.LineWrapExtensions, ",")
 	ctx.Data["BranchLink"] = ctx.Repo.RepoLink + "/src/" + ctx.Repo.RefTypeNameSubURL()
@@ -75,7 +75,7 @@ func CherryPickPost(ctx *context.Context) {
 		ctx.Data["CherryPickType"] = "cherry-pick"
 	}
 
-	canCommit := renderCommitRights(ctx)
+	canCommit := renderCommitRights(ctx, ctx.Repo.Repository)
 	branchName := ctx.Repo.BranchName
 	if form.CommitChoice == frmCommitChoiceNewBranch {
 		branchName = form.NewBranchName