Updates tmux config and vim bundles

I decided not to use irssi anymore, therefore the irssi window in tmux
has been removed.

The bundles for vim are now all bases on the github repos; specially
fugitive gave me trouble when I used the vim-script version.
More:
- the default colorscheme has changed to molokai.
- added tabular
- enable arrow keys again; not that I will use them though
...And some little adjustments in vimrc