Refactor input stuff

This is the start of a significant refactoring of everything related to sending messages, which is roughly:
- the chatbox
- action handling
- message sending on the c++ side
- autocompletion of users/rooms/emojis/commands/things i forgot

Notable changes so far include:
- ChatBox is now a ColumnLayout. As part of this, i removed the height animations for now. <del>as far as i can tell, they were broken anyway.</del> I'll readd them later
- Actions were refactored to live outside of the message sending function and are now each an object; it's mostly a wrapper around a function that is executed when the action is invoked
- Everything that used to live in ChatBoxHelper is now in NeoChatRoom; that means that the exact input status (text, message being replied to, message being edited, attachment) is now saved between room switching).
- To edit/reply an event, set `NeoChatRoom::chatBox{edit,reply}Id` to the desired event id, `NeoChatRoom::chatBox{reply,edit}{User,Message}` will then be updated automatically
- Attachments behave equivalently with `NeoChatRoom::chatBoxAttachmentPath`
- Error message reporting from ActionsHandler has been fixed (same fix as in !517) and moved to NeoChatRoom


Broken at the moment:
- [x] Any kind of autocompletion
- [x] Mentions
- [x] Fancy effects
- [x] sed-style edits
- [x] last-user-message edits and replies
- [x] Some of the actions, probably
- [x] Replies from notifications
- [x] Lots of keyboard shortcuts
- [x] Custom emojis
- [x] ChatBox height animations

TODO:
- [x] User / room mentions based on QTextCursors instead of the hack we currently use
- [x] Refactor autocompletion stuff
- [x] ???
- [x] Profit

src/actionshandler.h

@@ -5,13 +5,11 @@
 
 #include <QObject>
 
-namespace Quotient
-{
-class Connection;
-}
+#include <events/roommessageevent.h>
 
 class NeoChatRoom;
 class CustomEmojiModel;
+class NeoChatRoom;
 
 /// \brief Handles user interactions with NeoChat (joining room, creating room,
 /// sending message). Account management is handled by Controller.
@@ -19,56 +17,29 @@ class ActionsHandler : public QObject
 {
     Q_OBJECT
 
-    /// \brief The connection that will handle sending the message.
-    Q_PROPERTY(Quotient::Connection *connection READ connection WRITE setConnection NOTIFY connectionChanged)
-
-    /// \brief The connection that will handle sending the message.
+    /// \brief The room that messages will be sent to.
     Q_PROPERTY(NeoChatRoom *room READ room WRITE setRoom NOTIFY roomChanged)
 
 public:
-    enum MessageType {
-        Info,
-        Error,
-    };
-    Q_ENUM(MessageType);
-
     explicit ActionsHandler(QObject *parent = nullptr);
-    ~ActionsHandler();
-
-    [[nodiscard]] Quotient::Connection *connection() const;
-    void setConnection(Quotient::Connection *connection);
 
     [[nodiscard]] NeoChatRoom *room() const;
     void setRoom(NeoChatRoom *room);
 
 Q_SIGNALS:
-    /// \brief Show error or information message.
-    ///
-    /// These messages will be displayed in the room view header.
-    void showMessage(ActionsHandler::MessageType messageType, QString message);
-
     void roomChanged();
-    void connectionChanged();
+    void showEffect(QString effect);
 
 public Q_SLOTS:
 
     /// \brief Post a message.
     ///
     /// This also interprets commands if any.
-    void postMessage(const QString &text,
-                     const QString &attachementPath,
-                     const QString &replyEventId,
-                     const QString &editEventId,
-                     const QVariantMap &usernames,
-                     CustomEmojiModel *cem);
-
-    /// \brief Send edit instructions (.e.g s/hallo/hello/)
-    ///
-    /// This will automatically edit the last message posted and send the sed
-    /// instruction to IRC.
-    void postEdit(const QString &text);
+    void handleMessage();
 
 private:
-    Quotient::Connection *m_connection = nullptr;
     NeoChatRoom *m_room = nullptr;
+    void checkEffects();
 };
+
+QString markdownToHTML(const QString &markdown);