Members are now const-correct.
Replaced compile-time constants with enum.
Refactored common functions from Timer to Scheduler.
Disabled timer-precision unittests as they misfire often.

These changes are non-functional.

Change-Id: I6bb3d9fc402cadd556d9063ed9a4888f114c73d7
Reviewed-on: https://gerrit.libreoffice.org/17977Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>