Move color scheme fixes to User directory

[tdhsmith]

Package Control users utilizing the 'fix color scheme' feature would have their schemes overwritten on every update, leading to an annoying 'missing color scheme' popup. This moves future fixes to the User folder to avoid deletion.

Since the issue affects this update as well, there is also a small function to fail a bit more gracefully, reverting missing themes to Monokai rather than generating endless dialog boxes (which is Sublime's ridiculous default behavior).

Fixes #68

[tdhsmith]

(I'm going to test this on other OSes first.)

[jbrooksuk]

Let me know once tested. Looks fine though.

[tdhsmith]

Seems good. Yeah it wasn't a big change but I want to test whenever I introduce a file system manipulation. :wink:

[tdhsmith]

I don't know if you prefer each change to have its own version, but FYI I'll be working on the HSL parsing issue in an hour or so.