Remove Airline.  Replace with Tabline/Statusline functions

- Airline was too heavy and was slowing down startup time too much.
  It's very pretty but I think mostly unnecessary and I wasn't
  interested in half of the information it displayed.  It's also too
  complex and has too many configuration options, I prefer my vim setup
  to be simple.
- Replace default seoul256 StatusLine hl group.  The default is ugly.
Move unimpaired custom mappings into one function
Change after-object mapping from A -> aa, "A" used in visual mode