Provide the library name while creating the library based request path.
Ensure 'themes' assets are loaded whenever 'resources' assets would also
be loaded.
Added some CSS content plug-in tests.
Created a specific version of the bundleResources() method for
DeepAssetLocation, which cause the currently failing CSS content plug-in
tests to pass.
Simplified the DeepAssetLocation.seedResources() method, which was
previously folded inside out.
Added another failing CSS content plug-in test.
Modified the DeepAssetLocation class so it no longer leaks information
about the private ShallowAssetLocation instances that it is comprised of
internally, causing the failing CSS content plug-in test to be fixed.
Modified the CSS content paths we now produce so that we're no longer
targeting the old CSS bundler, plus started fixing bug this highlighted.