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/notificationsmanager.cpp

@@ -16,6 +16,7 @@
 #include <jobs/basejob.h>
 #include <user.h>
 
+#include "actionshandler.h"
 #include "controller.h"
 #include "neochatconfig.h"
 #include "neochatroom.h"
@@ -73,7 +74,7 @@ void NotificationsManager::postNotification(NeoChatRoom *room,
         std::unique_ptr<KNotificationReplyAction> replyAction(new KNotificationReplyAction(i18n("Reply")));
         replyAction->setPlaceholderText(i18n("Reply..."));
         connect(replyAction.get(), &KNotificationReplyAction::replied, this, [room, replyEventId](const QString &text) {
-            room->postMessage(text, room->preprocessText(text), RoomMessageEvent::MsgType::Text, replyEventId, QString());
+            room->postMessage(text, markdownToHTML(text), RoomMessageEvent::MsgType::Text, replyEventId, QString());
         });
         notification->setReplyAction(std::move(replyAction));
     }