Display information in status bar

When enabled, display in the status bar :
 - the current branch
 - the number of lines inserted or modified
 - the number of regions deleted

This option can be disabled so that GitGutter does not display any
information in the status bar.
Stop creating a directory thats not used

Don't remember why we were creating the **"Theme - Default"** directory,
we don't appear to be using it anywhere and GitGutter seems to work just
fine without it.
Merge branch 'master' of github.com:jisaacks/GitGutter
Don't show the current branch by default

Since retrieving the name of the current branch is an expansive
operation, GitGutter doesn't show it by default.

The `show_status` flag now accepts three values :
  - `none`, where no informations are added to the status bar,
  - `default`, GitGutter will show how many lines have been
    inserted and modified, how many regions have been deleted
    and what we are comparing against
  - `all` where it will also show what is the current branch.
Fix pep 8 formatted (lines can't be over 80 cols)
Merge branch 'duhem'