Remove ColorTable.hxx

The ColorTable header was split into two files: the normal ColorTable.h header and a secondary ColorTable.hxx that contains the ColorTable "implementation." This is so you can include ColorTable.h without necessarily having to use a device compiler.

However, this implementation is confusing. So ColorTable.hxx has been deleted and moved elsewhere. This means that the Sample method implementation is moved to ColorTable.cxx. Compiling these methods into the library makes more sense anyway. It also means that the Map methods have been moved to free functions and placed in a ColorTableMap.h header.