Add new RPC call, wallet_account_update_active_key and regression test

Add a new call to update the active key and write a test to verify that
it completes successfully and can be imported into a new wallet. More
testing is necessary.
Fix is_unique_account wrt updated active key

Previously a wallet account was considered different from its blockchain
counterpart if the active key had been updated. This is no longer the
case.
Add regression tests mentioned earlier

Oops, forgot to check these in... :]
Merge branch 'develop' into update_active
Basically redo a8f6808928eb5aa63d6b07738b789489e1898794
Update regression test: update_active_key
Some fixes wrt importing active key for registered account
Implement wallet scanning for updated keys
Fix bug in how wallet_db stores account records and update tests

Previously, the account record was stored only by account address, but
not by active addresses. This caused problems when the active address
did not match the account address. This is now fixed.

Also, add tests to verify that sending a transaction to an account with
an updated active key is working properly.
Add regression test for update_active_key: transfer from updated account
Merge branch 'develop' into update_active
Merge branch 'develop' into update_active
Merge branch 'develop' into update_active
Fix update_active_key regression test
Merge branch 'develop' into update_active
Merge branch 'develop' into update_active

Conflicts:
	libraries/wallet/wallet_db.cpp
Fix update_active_key test
Rework wallet use of active vs owner keys, update tests

The way I was adding the owner key to the wallet was inelegant and
hackish. I've changed the logic here to be much cleaner and more
flexible. In addition, the wallet was using the owner key for all
operations; now, it uses the active key for these operations.

I've also updated the tests, but I don't think the behavior is quite
correct yet.
Merge branch 'develop' into update_active

Conflicts:
	libraries/wallet/wallet.cpp
Fix update_active_key regression test