A lot of good stuff, like support for .hbs/.handlebars, comments, this-references

Sorry for the large commit, was on fire late this evening and fixed a lot of things in one huge commit..

Changes include:
- Support for .hbs/.handlebars if running Brackets Spring 38 or later (we got a new API to take back extensions mapped to other languages!)
- Support for handlebar comments {{! comment }} and {{!-- comment --}} (the latter supports having }} in the comment)
- Support for / and . in handlebars paths (ie referencing ./name to get the name property even if there is a helper called name) and the @index/@key properties in each-loops.
- Fixed usage of global CodeMirror-object, Brackets issues a deprecation-warning everytime you access it.

I've only tested it on Sprint 38 though I do some feature-detection to check for the new removeFileExtension-api so it should work with older versions as well.