Use neocomplete instead of neocomplcache

Update corresponding neosnippet config values. Also note that
neocomplete requires a vim built with lua, so e.g. on OSX with
homebrew you would just do:

`brew install vim --with-lua`

On ubuntu the `vim.gnome` build includes lua (`/usr/bin/vim.gnome`).
Use reverse tab completion order
Update vimrc organization and remove cruft