During integration of JVET-R0324, mvd_l1_zero_flag was moved down
in the syntax table (see JVET-R2001-v2). This change had not been
reflected in the !1563.

These changes should not affect any bitstream

In encoder, when automatically selecting profile, choose a still
picture profile when the level is 15.5 and a single picture is to
be encoded.
In decoder, don't check for single picture constraint when looking
up profiles.

gci_no_rectangular_slice_constraint_flag,
gci_one_slice_per_subpic_constraint_flag,
gci_no_subpic_info_constraint_flag and remove
gci_one_subpic_per_pic_constraint_flag

(1) move frame_only_constraint_flag and single_layer_constraint_flag outside the GCI syntax structure into the PTL syntax structure
(2) rename single_layer_constraint_flag to multi_layer_enabled_flag
(3) change ptl_alignment_zero_bit to ptl_reserved_zero_bit

JVET-S0066: gci_three_minus_max_log2_ctu_size_constraint_idc and gci_no_luma_transform_size_64_constraint_flag

Rename syntax elements to match spec and add range checks.
This should address JVET-S0130 aspect 1 (JVET-S0144 item 9.a)

Also fixes #738

- Rename members of WPScalingParam to conform to guidelines
- Avoid casts from const to non-const types
- Modify getWpScaling function to handle case where the reference
  index is negative (see #733)
- Add helper function isWeighted to determine whether weighting
  parameters are present for any colour component
- Fix some indentation issues