Allow disabling phone lock after enabling developer mode

Using a dedicated device for developing on Ubuntu Touch which doesn't ever leave the room and has no sensitive data on it, it would be great to have a way of accessing adb but still not being required to enter the device pin lock every time one wants to test something. This is really just a waste of time not adding any value from a security point of view. On such configuration's people will set the pin to something like 1111 anyways so I think we should spare them the effort of entering the pinlock every time the Greeter is swiped away.