Bug fixes and new features for LedgerTool.

* Fix RIPD-509, RIPD-514, RIPD-519, RIPD-525, RIPD-527, RIPD-529,
  RIPD-530 and RIPD-531.
* Protect people from ledger-spew and remove cruft.
* Better error messages and handling.
* Cache command lists or clears ledger cache.
* Better ledger summaries.
* Offline mode.