motion: remove trivial set methods; make some members public
search: keep AMVP candidates in mode structure

This fixes some work replication in --pme and will also make handling BIDIR
as a seperate prediction easier.
analysis: delay initialization of prediction cu until just before use

This avoids initializing CUs that may never be used because of various
early-outs
fix typo
analysis: delay initialization of prediction cu in RD 5 and 6
reference: add methods for querying CU/PU pointers
search: fixup