Add getThemedResourcesForApplicationAsUser()

Change-Id: I90b7cb441e4056f59b7260ffa55e31eba644e25a
Allow specifying a theme when creating a Context

A Context normally loads the resources associated with the given
package that this context is for.  This patch allows us to specify
a theme we want attached to a given context's resources.

Change-Id: I1e619f038566233bd89ee96eb8eb87fa6894e630