The new method allows processing sending errors that happen when sending from other places of plugin
then from the Sending Queue worker.
After three failed attempts it pauses the sending and admin user will see an notice.
[MAILPOET-4736]
Recently we've stopped incrementing sending counter when site configured to use MSS.
This caused that also code reseting the sending error was skipped.
This commit changes incrementSentCount method so that it always clears error log.
[MAILPOET-4448]
Before this commit, we used to calculate whether the sending limit was reached
by simply counting, how many emails where sent and when we did send them the
last time. In case the last time we did send was before the sending frequency,
and we reached the limit we would reset the calculation.
This led to the following problem:
In case we had e.g. one email send at an outdated timestamp, we would first fill
the outdated timestamp and once we reached the limit, we would reset the counter
and start with the current timestamp. So it followed, we would send more emails
than the limit would allow for.
[MAILPOET-4122]
