Allow to run Vim, Neovim and SpaceVim

Summary:
SpaceVim is a distribution of plugins for Vim and Neovim.

The final installation is to be done at user level, but there are some
preparation we can automate in config:

• install neovim and Python support
• ensure tmux supports true colors

Ref T295

Test Plan: nvim on WindRiver, then install Spacevim

Reviewers: dereckson

Reviewed By: dereckson

Maniphest Tasks: T295

Differential Revision: https://devcentral.nasqueron.org/D2647