Add some standard time sources, and remove the miscellaneous trait

This primary motivation for this pull request is to provide a nice default time source for execution, and package the time source functions up a bit more nicely for the maestro execution api, while maintaining backwards compatibility for the old job api. However, it also closes #238.
Ok maybe don't change it here. 

Should we mention that we use UTC in the documentation? I happy that we have a separate issue to track this problem.