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.