CMake build system refactoring

[Mc-Zen]

Changes

• Add some CMake options
  • Option for enabling IDE folders which sorts all projects into folders (default off to make it as it originally was). All libraries are put in a "C74_Libraries" folder, externals in a "Projects" folder and unit tests in a "Unit Tests" folder.
  • Option for building example projects (default on).
  • Option for surpressings automatic cmake regeneration (default on because this was set originally).
• added c74_add_project.cmake file with command c74_add_project() to replace includes of the pre and post scripts. The library output directories are set here instead of in the max-pretarget.cmake which makes more sense because the path lies in the min-devkit folder, not in the max-sdk-base.
• add min-api as subdirectory to bring all targets and functions into scope. min-api can still be a totally independant repository. The change here is that the option BUILD_DOCUMENTATION is available. Suggestion: we could add a if(PROJECT_IS_TOP_LEVEL) in the CMakeLists.txt file of min-api to only supply that option when min-api is built on its own.

[Mc-Zen]

I forgot to note:
Each projects CMakeLists.txt can now be replaced with something like

# Copyright 2018 The Min-DevKit Authors. All rights reserved.
# Use of this source code is governed by the MIT License found in the License.md file.

set(target min.beat.pattern)
c74_add_project(${target} SOURCES ${target}.cpp)
c74_add_auto_unit_test(${target})

I tried that out with all the default projects and they all work fine. Some have additional CMake code but this is no problem.

Of course I didn't want to push these changes until you said you'd want to migrate all projects to this new solution.

Best regards