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/customemojimodel.h

@@ -5,47 +5,46 @@
 
 #include <QAbstractListModel>
 #include <memory>
+#include <QRegularExpression>
 
-namespace Quotient
-{
-class Connection;
-}
+struct CustomEmoji {
+    QString name; // with :semicolons:
+    QString url; // mxc://
+    QRegularExpression regexp;
+};
 
 class CustomEmojiModel : public QAbstractListModel
 {
     Q_OBJECT
 
-    Q_PROPERTY(Quotient::Connection *connection READ connection WRITE setConnection NOTIFY connectionChanged)
-
 public:
-    // constructors
+    enum Roles {
+        Name,
+        ImageURL,
+        ModelData, // for emulating the regular emoji model's usage, otherwise the UI code would get too complicated
+        MxcUrl,
+    };
+    Q_ENUM(Roles);
 
-    explicit CustomEmojiModel(QObject *parent = nullptr);
-    ~CustomEmojiModel();
-
-    // model
+    static CustomEmojiModel &instance()
+    {
+        static CustomEmojiModel _instance;
+        return _instance;
+    }
 
     QVariant data(const QModelIndex &idx, int role = Qt::DisplayRole) const override;
     int rowCount(const QModelIndex &parent = QModelIndex()) const override;
 
     QHash<int, QByteArray> roleNames() const override;
 
-    // property setters
-
-    Quotient::Connection *connection() const;
-    void setConnection(Quotient::Connection *it);
-    Q_SIGNAL void connectionChanged();
-
-    // QML functions
-
     Q_INVOKABLE QString preprocessText(const QString &it);
     Q_INVOKABLE QVariantList filterModel(const QString &filter);
     Q_INVOKABLE void addEmoji(const QString &name, const QUrl &location);
     Q_INVOKABLE void removeEmoji(const QString &name);
 
 private:
-    struct Private;
-    std::unique_ptr<Private> d;
+    explicit CustomEmojiModel(QObject *parent = nullptr);
+    QList<CustomEmoji> m_emojis;
 
-    void fetchEmojies();
+    void fetchEmojis();
 };