Deactivate/remove unused portions of xolox and rename it.

xolox has a lot of good stuff in it - it's tried and tested, but we don't need all of it.
For example it highlights URLs in markdown/comments. That should be a completely separate plugin.
(It's a great feature - you can run `:Open` on any link and it opens it in the browser etc)

Start by inspecting how xolox is integrated into vim-reasonml, especially the URL-highlighting behavior and the :Open command described in the issue. Determine which portions are needed, separate or deactivate the unused features, and confirm the remaining plugin is consistently renamed.

Written by the indexing model from the issue text.