Increase Intervals for connectivity checks

[SurfingNerd]

This is effectivily a rollback of #313 - but we should keep the separation of connectivity timer from other hbbft engine timers.

Once the problem is fixed for the empty block #309 we should increase the connectivity checks, so the early epoch end system works fast, if the blockchain is under load.

The disconnectivity checks are already implemented as message queued solution. a further improvement could be, that it does not work timer based at all.
it could trigger:

• by detection by the hbbft message memo
• after block import.