Move ClarityBitcoinClient

[friedger]

The file ClarityBitcoinClient should be in the main source folder.

Commented code should be removed.
Documentation would be nice.

[bgok]

Marking this as an enhancement since it ClarityBitcoinClient is a thin wrapper around callReadOnlyFunction() from @stacks/transactions. It wasn't intended to by part of the API. I'm not opposed to adding later, but it will take a bit of time to write tests and documentation, so punting for now.