"Professional CMake" book suggest the following:
"Targets should build successfully with or without compiler support for precompiled headers. It
should be considered an optimization, not a requirement. In particular, do not explicitly include a
precompile header (e.g. stdafx.h) in the source code, let CMake force-include an automatically
generated precompile header on the compiler command line instead. This is more portable across
the major compilers and is likely to be easier to maintain. It will also avoid warnings being
generated from certain code checking tools like iwyu (include what you use)."
Therefore, removed the "#include <PreCompiled.h>" from sources, also
there is no need for the "#ifdef _PreComp_" anymore
Refactored code to support local and external material sources
This is the first PR in a series to support external modules. External
modules allow materials to be stored in external data sources such as
databases or web services. No new functionality is introduced in this
PR, rather it is a refactoring of code that will allow for changes to
be introduced in future PRs. Minor performance improvements have also
been made in the model and material managers.
The Python API has been enhanced for many data types to allow for
modification within Python.
