ensure new node listeners are at same tip as manager before adding to global listener

[johncantrell97]

There's a potential issue where if a block is connected after we synchronize_listeners for a new node but before we add it to the global chain listener then the new node listeners will miss that new block.

This issue is more likely to arise if bitcoind is still catching up to tip and is connecting blocks very quickly.

the solution is to

• bring node listeners up to tip
• pause polling the block source for new blocks
• ensure listeners are still up to tip
• add listeners to global listener
• resume polling block source for new blocks