NIFFile might not always be created from a file or stream containing NIF data.
Basically there are 2 different responsibilities for this class:
1. Read NIF file
2. Provide input for nifosg and bulletnifloader.
Remove no longer needed NIFFileMock since the state of NIFFfile can be
initialized independently from reading NIF file.
Objects no longer inherit from extra data class
"Controlled" harmful abstraction no longer exists
Introduced NiParticleModifier/NiParticleCollider abstractions
Extra data size reading moved into the base read() method
