Implicitly infer the number of MMVD base merge candidate to be 1 as MaxNumMergeCand being equal to 1, and mmvd_merge_flag is not signalled in this case.

- tiles are in the VVC spec for 3 meeting cycles now
- cleanup helps with adaptation for tiles to current draft

keep max TU in #define for possibility of keeping the parameter

TU max/min size are constants in the VVC draft. Reflecting this in the software.

  - Fix bug with previous solution for invalid Sub-PU TMVP issue.

fixes encoder/decoder mismatch with slices enabled, when merge candidates
are determined and the neighborig partition is triangle

also relevant for current tile design

Fix ticket #153 on using uninitialized interDir and GBI array when MaxNumMergeCand=1 and MMVD uses the second merge candidate as base MV.

  - Sub-PU TMVP can generate an invalid inter candidate.
  - Simplify previous solution and eliminate duplicated code.

  - Sub-PU TMVP can generate an invalid inter candidate.

  - Triangle merge list zero-MV candidates not properly initialized.

- all elements of SPSNext are moved into SPS
- syntax elements of SPS are sorted according to draft (as far as possible)
- comments were added where software and draft diverge