Add support for Command-T
Add support for csv files

Equivalent to airline csv Christian Brabandt plugin integration, but uses Python
own facilities.

Note: filetype detection is out of the scope of the powerline responsibilities.
      CSV is supported by powerline, but only as long as filetype detection is
      done by Vim correctly. By default CSV files are neither detected nor
      highlighted.

Some known differences between powerline code and @chrisbra plugin with
corresponding airline integration:

1. Detection work differently. I cannot say which is better because I have not
   tested it much, but it is definitely different.
2. My variant is able to detect whether there is (no) header. (Of course,
   relying on Python code.) Airline is using a setting. (Both do not allow
   manual per-filetype setting.) Of course, user can force either variant (no
   headers at all or headers always).
3. My variant makes it possible to configure header output format, including
   truncating it at 15 characters (the default).
4. CSV plugin does not work with multiline CSV items (in some dialects one can
   use code like `abc;"I<CR>am<CR>multiline<CR>string"`). See `:h csv-column` on
   how to fix this if possible (will require also changing `<sid>WColumn`
   function because currently it only works with one line).
5. AFAIK Python does not such a thing as “fixed width CSV”. Thus I do not work
   with this, but CSV plugin does. Not sure whether it is different with
   space-separated CSV files though.
Add support for capslock plugin