Remove debugging output
Callback support for targets from kwargs

Add an old workaround that appears to be no longer
needed and make it possible to use the cancellable
callback for targets specified in kwargs.
Convert tile download manager to ModRanaThread
Callback needs to be set to None in init

Or every thread will be considered trackable
and the thread removed signal will fire for each
one of them even if they are background worker threads.
Use ModRanaThread for tile storage loader