added change UserName, UserEmail and deletebranch

Content of this PR:

- now it's possible set the `user.name` and `user.email`
- it's possible delete local branches clicking the `x` near the name of the branch in the branch selector
- it's possible create a new remote
- it's possible delete an existing remote clicking the `x` near the name of the remote in the remote selector
- `askQuestion()` now supports default values inside its field.
- added a button to undo the last local commit
- The "close not modified" button was moved near the "Working Files" list. https://github.com/zaggino/brackets-git/issues/250