#5 Modularize CMake files

[Patrick M. Niedzielski]

We have a lot of duplication between our CMake files, and each one doesn't have a very clear goal. Here's what we should be doing:

• Each CMake file should do only one thing. They should be self-explanatory to modify.
• Remove checks specific to the compiler, if we can. This will help with supporting as many compilers as we can (GCC, Clang, and MSVC at the moment, Clang's cl interface and ICC in the future?).
• We should better use the CMake build types. Right now, we use only Debug and Release, and not very well at that.

This has low priority, but doing it will potentially make it easier to port the engine to new platforms and give users better diagnostics when the configuration fails.

[Patrick M. Niedzielski]

Started this work tonight.

[Patrick M. Niedzielski]

Fixed in commit 288659a87a63d35a4f72c645ff1a0524343cdc27. Marked as pending until next round of nightly tests.