Handle keyboard shortcuts at plugin load time

Don't load plugins based on keyboard shortcuts, as this conflicts with
vim-which-key. Instead, create shortcuts when plugins are declared, and
load them when the commands they provide are used.

plugins/ctrlp.vim.cfg.vim

@@ -1,6 +1,2 @@
 let g:ctrlp_working_path_mode = ''	" Disable CtrlP-controlled chdir
 let g:ctrlp_map = ''			" Disable default mapping
-
-nnoremap <Leader>pp :CtrlPBuffer<CR>
-nnoremap <Leader>po :CtrlPMRUFiles<CR>
-nnoremap <Leader>pi :CtrlP<CR>