request #7385: Burndown with a big remaining effort tree issues (cache)

If the burndown is configured to use cache, all values for past dates are cached and retrieved when needed.
Only the value for the current day is calculated at run time.

Change-Id: I61a4442ebb99733254f7a39a83294a6ec4b700b3
Merge commit 'refs/changes/05/3105/7' of ssh://gerrit.tuleap.net:29418/tuleap into HEAD

* ssh://gerrit.tuleap.net:29418/tuleap:
  request #7385: Burndown with a big remaining effort tree issues (cache)

Change-Id: I7ff5b2402ae459f4964c50092d1e2aa92c8bd437
This is Tuleap 7.7.99.69

Change-Id: I622ad8d1559cffd2cf226695dfa3f851df0d91e2