Change "+" icon under "Files" section to have three options:

* Create file
* Upload file
* New directory

Upload file is no longer accessible from the "Create file" page.
Users can now select a target branch in upload file as well.

Closes #2799: Fixes a bug where file modes were overwritten after a commit

Closes https://github.com/gitlabhq/gitlabhq/issues/8253: Existing files
can no longer be overwritten in the "Create file" section.

Closes #2557

Dynamically adjust placedholder for uploads and fix Dropzone event handlers

Override error handler to prevent error messages from being inserted underneath image preview

Fix tests

Use regexp instead of startsWith for better browser compatibility

Remove duplicate code in _replace.html.haml and use one template

Remove files upon error and retain alert messages until user adds a new file

    Refactor upload and replace functionality

    Rename file and move CSS

    Fix typo

    Make dropzone a div

    Remove unnecessary file

    Change color of "upload existing one"

    Add missing changes