- add MemoFormat property for memo
- MemoFormat and MemoType must be valid ASCII
- Memo content is converted on the serialization level
- add parsed_* version of Memo content if the parser understand the format
- support `text` and `json` MemoFormat
remote was instantiated as an object and checks through the class for `this.remote` would pass and cause
unintended behavior
e.g. `.complete()` would view an undefined remote as untrusted and not allow local signing
e.g. calling `_computeFee()` with an undefined remote would crash ripple-lib
