define common and generic item counters

to be used from tests (as an example offline count from sm_SUITE)
check server purity after suite

print warning message if the state is not clean
use escalus from branch travis-full-spec
clean last_activity after anon user

this should be cleaned by anonymous_purge_hook
but after this hook there is unset_presence_hook run
which sets the last_activity info back...
manually clean last_activity after user connected over BOSH