Ticket Support

This is the implementation of tickets, as described in https://ripple.com/wiki/Multisign, which is required for M-of-N work.

A set of integrations tests to check ticket creation, lookup and deletion will be needed and will be pushed into this request as soon as they are done. 
This is still a problem, due to an assert in [TransactionMeta::addRaw](https://github.com/ripple/rippled/blob/develop/src/ripple/module/app/tx/TransactionMeta.cpp#L229)

```c++
 assert ((mResult == 0) || ((mResult > 100) && (mResult <= 255)));
```

Any reason all my comments were deleted? Doesn't seem like there's been a force push