Cleanup and trim db migration process

Cleaned up the db version check wording, raise SystemExit exception with message to match how we handle other startup issues.
Added db version min check since we no longer are going to support migrating 2+ year old dbs.
Trimmed down the SB db migration process to only support build 496+ (2012-06-28) -- which covers the major migrations but allows us to eliminate a lot of legacy things that were not done correctly.
Updated initial db schema to latest (based off build 501).
Handle initial db creation compare against the min db check, optimize logic to hit the DB fewer times.
+ PEP8 fixes for db.py
Move database version check into InitialSchema

+ Change some variable names
+ Remove legacy BEST, not in mainDB upgrades anymore