Improve transaction fee and execution logic (RIPD-323):
* tecINSUFF_FEE if balance doesn't cover fee
* Ensure transaction recovery is deterministic
* Reduce transaction retries
Remove SHAMapNodeID from SHAMapTreeNode (RIPD-347)
This resolves the "right data, wrong ID" issue in the
tree node cache.
Freeze flags: (RIPD-394)
 * Define all flags
 * Set/clear bits in transactors
 * Frozen line counts towards reserve, is non-default
 * Report trust line state
Update freeze tests
* Conditionally skip freeze enforcement tests
* Honour remote.fee_cushion setting
* Workaround ripple-lib regression
* Don't use mocha features from wrong version