* Implement proposal validation
Includes commits:
Implemented CProposalValidator
Use CProposalValidator to check proposals at prepare and submit stages
Modify proposal validator to support numerical data in string format
Multiple bug fixes in governance-validators.cpp
Fixed bug in CheckURL
Fixed stream state check
Increase strictness of payment address validation for compatibility with sentinel
Improved error reporting
Implemented "check" rpc command to validate proposals
Fixes to RPC check command
Fix error message
Unit test and data files for proposal validator
Added test cases
Removed debugging code
* Fix name validation
* Changes to address code review comments
