Added Plugins.

Added the bessesary set of plugins.
Modified Vimrc for theme stuff.

Still a little buggy; the AirlineTheme errors out, so I need to
investigate that.
Modified AirlineTheme to be correctly set.

This means that the theme doesn't error out; the `:AirlineTheme` command
is just syntatic sugar around setting the `g:airline_theme` variable,
and is not defined as a command until _after_ the `.vimrc` file is
loaded, so this is why it was erroring out. The correct procedure, as I
have discovered, is to set the global variable directly.
Modified tex.vim.

Added a line to tone down the level of syntax checking, to only trigger
on errors; saves from dealing with `whitespaceErrors` when dealing with
the algorithmic package.