Add vim-numbertoggle plugin

Add plugin for line numbering management from Jeff Kreeftmeijer.
https://github.com/jeffkreeftmeijer/vim-numbertoggle.git

Signed-off-by: Mathieu Anquetin <mathieu@anquetin.eu>
Add NerdTREE plugin

The NerdTREE is a plugin that presents a filesystem view inside of vim.
It is a work of Martin Grenfell and is available at:
    - https://github.com/scrooloose/nerdtree

Signed-off-by: Mathieu Anquetin <mathieu@anquetin.eu>