Recent updates

* Core: Use "Low S" checking in SignSignature and SignCompact signature to prevent signature malleability;
* Core: Additional script checkings to break signature malleability;
* Core: Multi-threaded script verification;
* Core: Add unspendable coins support;
* Core: Prevent import keys for watch-only addresses and vice versa;
* QT: Display amount of unspendable coins on overview page and getinfo RPC output;
* Replace current balance with amount of spendable coins on send coins page.
* RPC: Add parsed and raw checkpoint message data in gectcheckpoint output;
* RPC: getblock (hash, true) and getblockbynumber (height, true) are now returning a set of raw transactions instead of parsed tx representation;
* RPC: getinfo now returns amount of unspendable coins;
* RPC: add importaddress <novacoinaddress> call;
* RPC: add redeemScript to listunspent output and signrawtransaction input.