Fix event properties ignored when subscribing to change/archive events

Closes #740 (closed)

We choosed wrong default values for *_event_detect attr properties, and due to this events can be subscribed event if rel_* or abs_ properties are not set (since they are ignored). Regression in 10.1.0 and 10.1.1.

Fixed wrong default values: they must be True.

Add test to check that we cannot subscribe to the event if the attribute has no abs/rel thresholds.

BUT: I found, that ALARM_EVENT is special, and you can subscribe to it in any case.