Several bugfixes and updates:

- Flipped GHSCONTRACT/SCRYPTCONTRACT and GHS/SCRYPT, because the latter is more prominent
- Added support for Cloud Folding (PPD)
- Added more helpful information to exception messages
- Added static helper methods to verify whether a given string is a valid Eobot miner type or 24-hour rental type
- Added support to convert cloud to cloud (e.g. SHA-256 to SCRYPT)