Add vim undotree

Undo branch visualisation without the python dependency (like with
Gundo).

vim/plugins.vim

@@ -18,6 +18,7 @@ Plug 'haya14busa/vim-asterisk'
 Plug 'joonty/vdebug'
 Plug 'matchit.zip'
 Plug 'scrooloose/nerdcommenter'
+Plug 'mbbill/undotree'
 Plug 'terryma/vim-multiple-cursors'
 Plug 'tpope/vim-endwise'
 Plug 'tpope/vim-fugitive'

vim/settings/toggles.vim

@@ -13,3 +13,6 @@ nnoremap <silent> <Leader>s :set scrollbind! scrollbind?<CR>
 
 " Toggle line numbers
 nnoremap <silent> <Leader>n :set number! relativenumber! relativenumber?<CR>
+
+" Toggle Undotree
+nnoremap <silent> <Leader>u :UndotreeToggle<CR>