Fixes for deprecated functions

This fixes #13 and fixes #10, though the latter is going solely by the comments made in the issue. This might also resolve #12, but I am unsure (if it does, it means your unit tests now work with SplitView).

I figured I'd make these changes as they comprise the majority of the incompatibility this extension has with the newest versions of Brackets, and gives the next person who wants to help fix this a few less things to do. :)