changed mechanism for automatically clocking in and out by location/wifi: now every tracking method registers itself on activation (and unregisters at deactivation) - real events are only generated when the first tracking method clocks in (clock-in event) or when the last tracking method clocks out (clock-out event)

git-svn-id: file:///home/svnroot-zephyrsoft/projects/trackworktime/trunk@540 f37aa4ac-6963-46a2-a1ff-558a307fa857