bugfix: fix screen ghosting after swiping north/south in scroll mode
As swiping north/south will generate several pan gestures which will
set refresh mode to WAVEFORM_MODE_A2, we should explicitly do a full
refresh in order to switch refresh waveform from WAVEFORM_MODE_A2
to WAVEFORM_MODE_GC16 as in OnPanRelease.
Merge pull request #222 from chrox/master

bugfix: fix screen ghosting after swiping north/south in scroll mode