Remove all FEST dependencies

We replaced fest-assert with assertj, and fest-reflect with vanilla java reflection.  In order to remove fest-reflect, we had to change our public interfaces of Robolectric.directlyOn and RobolectricInternals.getConstructor, as these exposed fest-reflect objects.
Having these littered all over the code base is ugly. We should pull these common reflective access patterns into a helper file that handles rethrowing the checked exceptions so that we don't have to pollute all the calling code.