Refactoring of parametric decoding and rendering

After work with the external renderer, it became evident that the DirAC framework decoding and rendering structures, and many parts depending on it require refactoring work. Firstly, implementing external renderer without including most of the decoder is quite hard without this work. Secondly, memory is not used optimally in most cases as certain configurations do not require all the memory. This is noticed already in issues #123 (closed), #125 (closed), and #127 (closed).

This issue will cover the whole work and offer a shared branch to work with the issue. Subtasks follow individual topics and more might be added later on. The changes should be bit exact within the context of this issue and non-BE changes should be separated into a different issue.

• Refactor parametric binauralizer to be independent of hDirAC
• Refactor parametric ISM to use only relevant parts of hDirAC and possibly consolidate use of azimuth and elevation
• Separate DirAC bitstream decoding to a separate file. Also remove other possible dependencies between decoder and renderer
• Reduce dependency on st_ivas where possible