multiprocessing - allows to catch tests that are running too long.

Re: Looping #3 

It could easily be made to run different tests in parallel, but this might mess with tests that read or modify files or other assets.

- [x] Run each test in a separate process
- [x] Give an error and cancel it when lagging too long
- [ ] Meaningful tests (needs #5 fixed) 

Since the internal code running system got a little bit more complicated, to quickly point out where the issue is

- [ ] Internal (execution_base) tests