Extend them to CMakeLists.txt,
and bundle the checks in one CMake module.

cmake/bornagain/modules -> cmake/modules
cmake/bornagain/scripts -> cmake/configurables
cmake/generic/modules   -> cmake/extensions

The following fix is necessary to ensure that the Boost installation as
found by CMake will be used, instead of the one that is installed in
/usr/include.

Top-level routines moved from Fit/Suite to Core/Fitting.
Some base classes and utilities moved from Core to Fit/Utils. This requires more thought.

Restored unit tests (accidentally outcommented from test refactoring); repaired configure_file(MacOSXBundleInfo.plist.in): this resolves #1458.