Updated MergeNifTrees to handle some cross references (skin blocks).  Other blocks with cross references can be added by overloading the ABlock::ReassignCrossRefs function.

Added documentation to IControllerSequence.

Fixed ReadString function so that it can read strings with \0 characters in them.

* Support for all ten NiStringPalette offsets.
* There's still a problem with NiStringPalette: apparently the C++ string type does not allow null characters? ... Maybe we can try to find a workaround in the string reader function.

* Changed the radius algorithm.

Now the calculated center & radius values should correspond to the values found in official NIF files.

Brought NiControllerSequence up to date with DocSys, but commented out interface functions for later implementation.

Block implementation is current with DocSys again.

Small changes to constness of some functions.

Simplified the ITriShapeData and ITriStripsData interfaces slightly.

* fixed skeleton root calculation

Created classes for all new 20.0.0.4 blocks.
Re-implemented NiTexturingProperty as a data-style block.  Still needs an interface so is currently uncontrollable.