Implementation for this story https://trello.com/c/gbBtpARq/709-1-define-default-html-file-for-live-development

Implemented fix for https://github.com/adobe/brackets/issues/2033

Added a lot of test cases to cover the new functionality.
fixed some of the issues mentioned in the review
fixed some issues mentioned in the review

- added some forgotten waitsForDone() calls
- added a missing test case for dynamic-project-6
- check document and if it doesn't have a masterEditor before adding the document to the workspace
- removed the waits() call after invalidating the FileIndexManager
- re-enabled the message dialog if no suitable document was found for Live Preview
Merge pull request #5414 from adobe/irichter/open-default-html-for-live-development

Implementation for this story https://trello.com/c/gbBtpARq/709-1-define-default-html-file-for-live-development