resolve (most) mac static analyzer issues

This resolves most of the potential (and actual) memory leaks and other issues identified by the Xcode static analyzer. The only analyzer issues that I did not resolve are:

- brackets-shell/appshell/client_handler_mac.mm:419:7: Incorrect decrement of the reference count of an object that is not owned at this point by the caller
- brackets-shell/appshell/client_handler_mac.mm:430:1: Potential leak of an object

The reason I didn't make any changes here are because it appears brackets-shell is overriding a cef window delegate, as explained in the comment at client_handler_mac.mm:411, and the code is decrementing the cef delegate which we don't have ownership of BUT it is intentional. I left that code as-is for now because I did not see a simple way to resolve those two analyzer issues.

After running Instruments and looking for leaks, this update fixes quite a few leaks which were appearing when opening the app.

All Brackets Jasmine tests pass.