Xoo SCM should support relative dates

The Xoo SCM used in ITs loads custom blame information from text files in the project being analyzed. The supported format only allows us to specify absolute change dates.
This is problematic in some tests, because as the dates get older, certain housekeeping tasks get triggered, affecting the expected behavior of those tests.
We should also be able to define dates based on relative dates, like "-10d" (meaning 10 days ago).

Then, we should update the tests that we know can become unstable over tables with absolute dates.