Allow default paths to be overridden on bootstrap command line
Buildserver - rework scripts

- rename daily_build.* to build_periodic.* - none of the scripts can
  actually enforce daily building. That's done by a timed command in Windows
- add command line parameter to build_periodic.sh. If set to weekly
  only run the script on mondays.
- drop weekly_build.sh, periodicity is now added in build_periodic.sh
- rework build_tags.sh for the new build scheme