Implement todos in touchscreen generic plug-in.

Implement todos in touchscreen generic plug-in.

The patch implements periodic clearing of the point states when no
activity occurs (i.e. no ev_syn is coming at all, meaning that most
probably all the fingers are already up) and also moves the entire
functionality into a separate thread even when used as a plug-in.

Change-Id: Ib1daa738085b61af9b07eb8a284416e5a3fcabe8
Reviewed-on: http://codereview.qt.nokia.com/1744
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jørgen Lind <jorgen.lind@nokia.com>