Clean up intra mode search.

- This changes the bitstream a little bit, because it changes the order in
  which the modes are tried and when two modes have the same cost the first
  one is chosen.

- Dst buffer was removes as it was no longer used.
Move intra prediction generation to its own function.
Change intra reconstruction to use the same prediction function as search.

- This fixes a bug with intra search. It sometimes used filtered reference
  pixels for 4x4 blocks leading to inaccurate cost estimate.
Merge branch 'intra-cleanup'

Conflicts:
	src/intra.c
	src/intra.h
	src/search.c