Fix some deadlocks and sigsegvs
This MR builds upon the deadlock/sigsegvs PR at https://github.com/indilib/indi/pull/1243.
The first commit of the series is enough to either crash or deadlock KStars during execution of test_ekos_simulator
, with or without the indilib
PR.
Note: lambda signals connected without explicit receivers are not disconnected when receiver is deleted. This happens for instance in the clock propagation signal when a Property is deleted before its Device is deleted.