Dwell clicking shouldn't start until head is detected

[1j01]

trafficstars

Right now the dwell clicker can start before the camera stream has even started. Now, it may be desirable to use the dwell clicker separate from the head tracking, with an eye tracker, especially once I make the dwell clicker more useful with knowledge of system controls (#40) and controls on web pages (#27), but if the head tracker is enabled, the dwell clicker shouldn't start until the head is tracked.