Add Contrib and Fix Powerline Colours

This PR was intended to just be about adding my own contrib layer, but because I messed up on some Git stuff, it includes other things as well (which I originally intended to be separate PRs).

#### Changes Included
- Adds a `trishume` contrib layer which adds LaTeX and smooth scrolling support (more goodies to come)
- Fixes the issue mentioned in #21 about the powerline not having the right colours in inactive buffers
- The "custom" package added a section to `init.el` without asking. Maybe this should be in the repo so it doesn't keep inserting itself? Or is there some way to tell it to put this crap somewhere else (like .spacemacs)?

Also I'm back! Once XCode 6.1 was released on the app store I reinstalled emacs (24.4 now!) and am back to configuring it. Expect more PRs!