Upload filter automatically and use filter_id (#201)

When a custom filter is inserted into nheko.conf or there was no filter
defined yet the default filter gets automatically uploaded.
After a successful upload the server-side generated filter-id is used.

This is done async as it is just an enhancement and it is not required
to upload the filter before the first request.

include/MatrixClient.h

@@ -64,6 +64,7 @@ public:
         void uploadAudio(const QString &roomid,
                          const QSharedPointer<QIODevice> data,
                          const QString &filename);
+        void uploadFilter(const QString &filter) noexcept;
         void joinRoom(const QString &roomIdOrAlias);
         void leaveRoom(const QString &roomId);
         void sendTypingNotification(const QString &roomid, int timeoutInMillis = 20000);