vim: Move language specific bits into ftplugin/

Move stuff for specific languages executed by autocommands into own
filetype plugins to keep the vimrc cleaner.

.config/vim/ftplugin/gitcommit.vim

@@ -0,0 +1,4 @@
+" Shorter lines. Subject should be max 50 and body max 72
+setlocal colorcolumn=50,72
+" Spell checking always enabled
+setlocal spell spelllang=en_us