Migrating expts from experimental into playground

Migrates experiments from expeirmental to playground.
Included experiments are FILTERINTRA, MASKED_INTERINTER, INTERINTRA
and MASKED_INTERINTRA. Bugs in masked sub-pixel variance calculation
and masked sub-pixel motion search are fixed. Recursive filters for
intra prediction are upgraded to 4-tap filters.

Change-Id: I9964a7ebfefc1efa70bb66be7b35d975c3f66e23