SystemTimeStamp used to be an opaque class, as it was provided by
`system_{linux/other/windows}.h`. Because of this, code dealt in
SystemTimeStamp pointers, and getting the current timestamp required a
memory allocation. Now SystemTimeStamp is just a
`std::chrono::time_point`, we can make the code cleaner and faster by
just directly keeping SystemTimeStamp instead of pointers around.
* created a static library containing most source modules
to avoid compiling source modules twice in code and unit tests
* moved profile_test to main unit tests executable
* removed image_test and edit_test as not really useful
* all tests are now in /test/ subdirectory
* unit tests concatenated to one executable (TODO: ui, common)
* preparation for test environments (OpenGL and others)
* removed old TestCBot
AbigailBuccaneer