implement transaction expiration limits
transaction expiration, and optional scanning

Transactions now set a default expiration
There is now a wallet option to enable scanning for the purposes of unit
tests.
updating unit tests for scanning
implemented ability to upgrade to a delegate and reduce your pay
updating genesis block timestamp
reducing desired connection count to 8
adjust max block size to yield about 2 trx/sec maximum
in-memory cache of known transaction IDs used to accelerate validation
fix conflicts
updating fc