Re-factor bit allocation in first pass.
Restructuring to allocate the bits for each frame in a GF group at the time the group is defined. At the moment the allocation closely mirrors what we had before. Also changes the default rate adjustment method to LONG_TERM_VBR_CORRECTION. Change-Id: Ie5793c46c6b9c888cead5d8790792efd7d60b7c1