[Upstream] Fixing few shutdown problems

[lyricidal]

First commit was decoupled from #2131, the topbar staking status polling should not try to refresh data if shutdown was requested.
Second commit is coming from bitcoin#12377.
Third commit is starting the shutdown process and returning early (without starting the import thread) if the best chain cannot be activated during the node's initialization.

from PIVX-Project/PIVX#2228

fe398cc was slightly modified to only add the function, it is not currently in use, but can be useful for future