Enhancement: Flatten the Compare against Main Menu
Enhancement: Flatten the Compare against Main Menu

GitGutter provides the following menu items:

- Main Menu -> View -> GitGutter -> Compare Against -> HEAD
- Main Menu -> View -> GitGutter -> Compare Against -> branch
- ...

As the "Compare Against" menu item is almost the only one within "GitGutter" it makes reaching the desired ones unnecessarily complicated.

Therefore this commit moves all "Compare against" menu items up by one level in order to make them accessible more easily.

Furthermore it adds an entry to display the diff popup just for consistency.

jisaacks/GitGutter