Add retain service on storagenode. This service runs retain jobs that have been queued by the storagenodes. Rather than running retain jobs during the grpc Retain() call, the grpc call queues a retain job to the retain service and returns immediately afterwards, removing a significant bottleneck in garbage collection.
* add cache, update cache w/piece create/delete
* add service w/loop to cache to recalculate space used cache
* add piecestore cache to other sn svcs to use
* add table to persist the total space used
* rm cache where not needed
* rm stuff from sn svcs
* start fixing tests, changes per comments
* update commits
* add unit tests
* fix commiting before we write header bytes
* fix cache create test
* copy cache map, add started back to recalc
* fix test
* add test, update comments
* re-organizing into bandwidth service. re-enable rollup loop
* Prevent uniqueness failure in bandwidth rollup
* Add test to make sure the rollup select date range works correctly
* add bandwidth config for rollup interval
* add voucher service on storage node
* config field tag syntax, go routines for requests
* hook up voucher service in storagenode/peer.go
* add voucher config to testplanet
* add voucher config to testplanet
* add voucher response status INVALID, ACCEPTED, REJECTED
* add a test for vouchers service
* handle no row from GetValid, test it
* add trust pool to voucher service
* use trusted list to get satellites
* verify vouchers upon receipt
* test VerifyVoucher
