Add an option to overload the default F2 dependency loader

[markhealey]

We've received a number of requests for script/style loader override hooks be added to F2. I've written this as a story:

As a developer using F2, I want to be able to apply a custom script and/or style loader for F2 to request an app’s dependencies as defined in the AppManifest. This script and/or style loader would replace the built-in default App dependency loader in F2.

The proposed solution is as follows:

• Add two new properties to the F2.ContainerConfig called loadStyles and loadScripts both of which are optional.
• Both loadStyles and loadScripts would be functions passed an array of dependencies during the registration of an app.

@montlebalm actually wrote a lot of this code ~6 months ago, so we're in the process of digging that up and revisiting.

Spec updates to come.

[markhealey]

I meant to add this will be released in version 1.3.3 leapfrogging the proposed 1.4 work-in-progress tracked in #142.

[ilinkuo]

Thanks for making this visible.

[markhealey]

FYI we are planning to release 1.3.3 this week.

[markhealey]

Closed with #155