Determine startup order

[oubiwann]

The following need to be taken into consideration:

• The external included apps that need to be started
• The internal external apps that need to be started
• The operations that need to be performed as part of system bring-up
  • verifying required configuration data is present
  • performing any required database migrations
  • checking for available games in configured directory
  • hashing all game files and checking against those in the db
  • loading any missing files into the DB
  • adding any updated content to the DB
• The order in which all of these should be done

The first two are handled nicely by OTP releases, but the third will need some custom work and possibly the use of Erlang/OTP start phases (https://erlang.org/doc/design_principles/included_applications.html)

Blocks #46