Provide convenience of using profile address as billing address regardless of profile's placement on the contribution and / or event registration forms

Provide the convenience of a single address block regardless of whether the admin configured profile is above OR below the billing block:

1. Show checkbox regardless of whether profile is top or bottom.
2. Change checkbox text to "Use a different address for billing". Default state is unchecked (Billing Address is hidden)
3. Checking that box unhides the Billing Address block.