Adds a wiener filter based restoration scheme in loop which can
be optionally selected instead of the bilateral filter.

The LMMSE filter generated per frame is a separable symmetric 7
tap filter. Three parameters for each of horizontal and vertical
filters are transmitted in the bitstream. The fourth parameter
is obtained assuming the sum is normalized to 1.
Also integerizes the bilateral filters, along with other
refactoring necessary in order to support the new switchable
restoration type framework.

derflr: -0.75% BDRATE

[A lot of videos still prefer bilateral, however since many frames
now use the simpler separable filter, the decoding speed is
much better].

Further experiments to follow, related to replacing the bilateral.

Change-Id: I6b1879983d50aab7ec5647340b6aef6b22299636