Add the ability to open files with paths of the form "path[:lineNumber[:columnNumber]]"

This change, gives the ability for Brackets to open a file and then scroll to a selected line and column. This commit takes care of the necessary changes to the brackets project - there are also a couple of commits in the brackets-shell project. 

Implementation note: I considered 2 ways to provide line/column information: (1) encode the line and column number into the text of the path, or (2) pass line/column as separate parameters. Option #2 would have required changing numerous functions in both brackets and brackets-shell to pass this additional data, so I chose #1.

Testing note: this change includes some new unit tests for the parseDecoratedPath function. Also, I've added some comments to DocumentCommandHandlers.handleFileOpen() describing various manual tests.