Support for subclasses of android.content.res.Resources().

ShadowResources will use the application ResourceLoader by default. Only the System Resources will have its ResourceLoader explicitly bound.

Convert all references to resourceLoader instance member to using the accessor to ensure instantiation.

Add test which exposed an NPE for ShadowResources.resourceLoader and fix.
Merge pull request #1279 from jongerrish/shadow_resource_subclasses_should_have_app_resourceloader

Shadow resource subclasses should have app resourceloader.