Signalling of CPB timing parameters for sub-layers in DU-based HRD
operations
Remove pt_max_sub_layers_minus1 and use corresponding syntax element in
BP SEI
Make parsing of BP, PT and DUI SEI independent from SPS

- create own files for HRD classes
- rename HRD to HRDParameters
- create HRD class that can hold all HRD related parameters as base for encoder/decoder specific implementations