Extensions should load after the core Brackets UI is initialized

[jasonsanjose]

In #943, extension loading was changed to support extension unit tests. This change was made to ensure the test Brackets window was fully initialized before the test begins execution.

Issue #954 shows that extension load failures now crash Brackets on init.

Brackets should revert to it's old behavior of completely loading the UI before loading extensions. To support unit tests, we will fire a new event (or some equivalent) to ensure extensions are loaded before extension unit tests execute.

[pthiess]

I agree this needs to be fixed in this sprint, I may even have proposed it being a high priority bug due to it's impact.

[jasonsanjose]

Closing.

[peterflynn]

Note: ordering extension loading this way is now much less critical because #1968 makes us able to catch errors that occur during extension loading.