Improve console output

[arkpar]

Fixes #3269

• Cache idle state in sync so that requests are not collected with every network poll.
• Block import are printed in the console by default
• Removed some additional console spam.

[twittner]

I think is_idle is touched in too many places and is too fragile to use. If only one self.is_idle = false is missing, block_requests will not function properly. Rather than introducing this flag I would consider removing the line trace!(target: "sync", "No new block request for {}", id);.

Generally speaking I think we should make more use of the available log levels. I think it is okay for trace to produce a lot of output as it is meant to literally trace through the whole processing flow as it happens. We seem to be using info only rarely if at all so everything informational ends up in debug or trace. Maybe lifting most of debug to info and some of trace to debug would leave room for the truly noisy messages to be left on trace level.

[arkpar]

info is printed to stderr by default. We are already using it for important messages that user should see. I agree that is_idle is somewhat fragile. Having the request diagnostic is fairly important though as it already helped finding a few issues in the past.