modules: add new modules and new configurations

* Adds modules: mru, nerdcommenter, snipmate.vim, tagbar,
  vim-markdown.

* Modifies configuration for: ctrlp, default, nerdtree,
  python-mode.

* Adds configuration for: mru, nerdcommenter, tagbar.

Signed-off-by: Leonardo Rossi <leonardo.r@cern.ch>