Allow the avatar to be changed

This Merge Request allows an avatar to be set through the userEditSheet
The parts in controller.cpp decode the url and check whether the image
is valid, through qimagereader.

src/controller.h

@@ -50,6 +50,8 @@ public:
 
     Q_INVOKABLE void changePassword(Quotient::Connection *connection, const QString &currentPassword, const QString &newPassword);
 
+    Q_INVOKABLE bool setAvatar(Quotient::Connection *connection, const QUrl &avatarSource);
+
     [[nodiscard]] int accountCount() const;
 
     [[nodiscard]] static bool quitOnLastWindowClosed();