Support Token Issue and Token Burn in QT GUI

[Naviabheeman]

Only token transfer is possible using the current interface in tapyrus QT GUI. Colored coin support added by #201 to #206 does not allow token issue and token burn. These two transactions require special handling of transaction inputs and outputs in WalletModel::prepareTransaction() similar to how RPCs issueToken and burnToken before the call to 'CWallet::CreateTransaction'