Added org-repo-todo layer

This lets you use `SPC o c t` to add a todo header to the TODO.org file created at the root of your project and also lets you visit it anytime with `SPC o g t`
It is! but I didn't know whether to touch it or not... :( as the extensions.el comments said that there were gonna be loaded before/after the package.. :s @syl20bnr  is there anything wrong with deleting this packages.el?