Replace snipMate with UltiSnips.

The snipMate plugin hasn't been updated in a long long time, UltiSnips
seems to be the replacement to go for at the moment;

    - snipMate snippets are easily adapted
    - It "does" Python
    - snippets-in-snippets
    - ... and probably a ton more.
Moved snippets per file type into 1 file.

At first glance, it does not seem that UltiSnips supports multiple
snippet files per file type as snipMate did.
It might be that it does, but not that much out-of-the-box as I would
like it to be at this time, moving everything back in 1 file per file
type seemed to be the fastest workaround...