Implements;

• sync_version per plugin (if applicable)
• sync_version daemon wide (updates every time a plugin increases sync_version)
• polling based peer sync_version checking, re-syncing if changed from last time.
• docker: prevent crash on start when docker plugin fails to start, retry forever

Does not implement yet (scheduled for other issues/milestones);

• websocket event based incremental syncing
• single plugin syncing (currently everything resyncs from stratch every time)

Closes #89 (closed)