Enhanced polling action

* when resuming, tries first the previous task if present
* when error occurs while polling, retries several times before
  actually failing
* it allows to start with short polling intervals and increase that
  later
* less methods needed to define to actually start using it

For better testing, I've also made the testing logger non-singleton by
default, so that one can set log levels per test. Also, it's possible better
inspect the managed clocks now.