Add compound-singleref (compound mode using single ref)

This new coding tool is targeted to complete following two tasks:
(1) Remove the inter mode NEWFROMNEARMV;
(2) Add new inter coding modes that provide compound prediction but
    using single reference frame - initially NEAREST_NEARMV from
    single reference.

Change-Id: Ifadf91147d0b12c2f62cfd79a72ce0c37c4ee949
1 file changed