The logic of verifying a message was duplicated in 2 places:
src/qt/signverifymessagedialog.cpp
SignVerifyMessageDialog::on_verifyMessageButton_VM_clicked()
src/rpc/misc.cpp
verifymessage()
with the only difference being the result handling. Move the logic into
a dedicated
src/util/message.cpp
MessageVerify()
which returns a set of result codes, call it from the 2 places and just
handle the results differently in the callers.
