gcylc: fix task added by reload

This follows on from #1208.

Adding (and then inserting an instance of) a task by reload worked in the suite daemon, but two gcylc views couldn't cope with the result: the dot view would not show the new task; and the tree view would crash. This was caused by data structures representing the runtime hierarchy not being updated, in the GUI, after the reload.

This branch fixes the GUI and adds a test that passes on master too, but gcylc from master will behave as just described if you follow the test with it.

@benfitzpatrick - please review.