Replace vim-powerline with vim-airline

Signed-off-by: David Celis <me@davidcel.is>
Switch tmux to fish

Signed-off-by: David Celis <me@davidcel.is>
Update vundle

Signed-off-by: David Celis <me@davidcel.is>
Use vim-airline instead of vim-powerline

Signed-off-by: David Celis <me@davidcel.is>