Refactor action definition

- Make an empty message type optional mean "no message"
- Set message type for all actions that send a message through the normal mechanism
- Remove now redundant bool specifying whether a message should be sent

src/models/actionsmodel.h

@@ -30,18 +30,10 @@ public:
          * @brief The function to execute when the action is triggered.
          */
         std::function<QString(const QString &, NeoChatRoom *, ChatBarCache *)> handle;
-        /**
-         * @brief Whether the action is a message type action.
-         *
-         * If this is true, a message action will be sent. If this is false, this
-         * message does some action on the client and should not be sent as a message.
-         */
-        bool messageAction;
         /**
          * @brief The new message type of a message being sent.
          *
-         * For a non-message action or a message action that outputs the same type
-         * as its input, it's nullopt.
+         * For a non-message action, it's nullopt.
          */
         std::optional<Quotient::RoomMessageEvent::MsgType> messageType = std::nullopt;
         KLazyLocalizedString parameters; /**< The input parameters expected by the action. */