Replacing ItemUsageIndex with UsageLookup

This introduces the useLegacyUsageIndex option,
which for now is set to true per default.

If true, the new wbc_entity_usage table is not used
and not created by the updater.

Change-Id: I72d55b81f640d17b2969a6aa92350deb923b6fdb
Merge "Replacing ItemUsageIndex with UsageLookup"