Fix mistakes after previous merge and make it compile.
Rewrite the function interpolating between time stamps as it was
written after the original pull request was created. Add unit tests
for it.
I couldn't help myself and also changed some enums to enum classes and
did some renames.
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
MrSimbax