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.
No, `fromDirStructure` would be better ... I guess I just wanted to demonstrate (to myself as much as anyone) that the backwards compatibility worked. (Most people will just have a call to `timeFromPath` here, not `Maestro.timeFromPath`, which is why I changed that ... but either way no code changes were required).