Adds a metric for the Vaadin session count. The metric uses a gauge measurement, which automatically reports a specific value in intervals. This uses the Vaadin session count specifically, rather than HTTP sessions, I figure this is appropriate for what we want.
Description
Adds a metric for the Vaadin session count. The metric uses a gauge measurement, which automatically reports a specific value in intervals. This uses the Vaadin session count specifically, rather than HTTP sessions, I figure this is appropriate for what we want.
Closes #78