Peercoin fix.

* Added support for peercoin variants, fixes #442, resolves #410.
* Added block-explorer fields in coin config, fixes #476.
* Implemented a brand new coin configuration format; https://github.com/CoiniumServ/CoiniumServ/blob/develop/src/CoiniumServ/config/coins/README.md
* Updated coin configs against new format.
* Removed scam-coins with no websites & working block explores.
* Added coin config json validator script
* Improved WebServer.cs:UnhandledExceptionHandler().