Several things in this commit:
* Prior to this commit, libplab depended on db state to create slivers and slices. Now it can be done using the regular command line tools without the metadata in the db. This makes development and debugging much easier and allows us to use the command-line tools even if state has been cleared out of the db (i.e., for sliver garbage collection). * Add support for sliver start/stop/restart via the v4 NM. * Some support for sliver garbage collection. * Various other improvements and cleanup.