Added basic Git-FTP features.

Close this.

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This is the first draft for the support to [Git-FTP](http://git-ftp.github.io/git-ftp/).

Currently it adds two buttons on the right side (ftp init and ftp push).
My idea is to merge the **ftp push** with the current "git push" button and make it use the **Git-FTP** feature only if the FTP remote is selected (Git-FTP let us configure an "ftp remote" saved in the configuration).

Let me know if you have better ideas.

The only problem I've found is about the timeout: Git-FTP is not very fast and brackets-git goes in timeout often.