Activate all bundles before sourcing vimrc-before.vim.

This means all colorschemes are available for use directly in the
vimrc-before.vim script; it also introduces a small chicken-and-egg
problem for disabling bundles in vimrc-before.vim.  To solve this, a
vimrc-vars.vim script has been added.
Add Badwolf dark colorscheme.
Add Base16 colorscheme collection.
Add Gruvbox colorscheme.
Add Hemisu colorscheme.
Add Hybrid colorscheme.
Add Monokai colorscheme.
Add Wombat256i colorscheme.
Document new colorscheme bundles.