New structure for startup generator

New structure for the generator.

Replace the old linear start sequence. The linear structure could no longer support the desired multi-branched links between systemd units. For example, the IOP model should depend on both the dolphin daemon and the dolphin drivers.

The structure now is just objects associated with systemd units, with linkages that mirror the systemd unit linkages.

Everything is built up as a data structure, then dumped to the systemd unit files at the end. No more intermingling of sequence creation and file writing.

Complexes of units are handled by overarching classes. For instance, dolphin.py defines the Dolphin class that is responsible for all the internal linkages with the many dolphin units, including dolphin ports, dolphin driver and dolphin proxy. There are similar classes for handling model units, edcs, daq streaming.