Add Lists and HashMap for gravity wells and block protection

Used to speed up Listeners and hopefully reduce lag.
Put block locations into protect blocks HashMap. Make sure we are saving the door direction.
If we're rebuilding we don't need the database stuff...
Add command /tardis gravity to convert old gravity wells to new style

Will remove this command upon final release!
Use the new gravity_well table
Remove protect blocks from HashMap
New class to load protected blocks and gravity wells in to HashMap and Lists
Put block locations into protect blocks HashMap
Put the gravity well locations in the gravity Lists
Use the HashMap and Lists (instead of database lookups) to reduce lag