Add DOUBLETAP to events emitted when in single touch only mode.

Users with a single touch firmware report not seeing the DOUBLETAP events; this
is a side effect of dropping old mapping for confidence. The confidence mapping
may be fine for singletouch mode but causes problems in multitouch mode.
Signed-off-by: Rafi Rubin <rafi@seas.upenn.edu>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>