Fixes a few bugs and general cleanup
* Transactions are not cleared when pushing blocks, this was a bad copy and paste bug
* Locks are instated for extra safety. Make generating jobs and updating block template exclusive operations
* Fix for mm_later being None and crashing with no merged coins
* Fees are now calculated at block template building stage, not at job generation. Avoids mismatch between fees
* Work restarts for aux blocks are now handled properly. Job updates are different than new blocks...