Provide CMake building system

[Wohlstand]

• Make PGE File Library be buildable as static or dynamic library (as STL or as Qt variant)
• Organize source code files and public include files into separated "include" and "src" folders

I think, we would drop away support for Qt variant after reorganizing of PGE Editor and use STL only variant which is much faster than Qt.
What do you think about this, @KevinW1998 ?

Also, make this library to be licensed under MIT.

[KevinW1998]

I am fine with MIT license change and QVariant removal

[Wohlstand]

As "variant" I meant version of library where are widely used QString QVector, and related types. For now it is dual STL and Qt made by bunch of macros

[KevinW1998]

Yea, that's not really nice