Trigger zoom via pinch on touch display

[llemeurfr]

This should be possible on both FXL and reflow publications. In reflow mode, it would results in a font size modification. In FXL it would be a zoom on the webview, with a way to move inside the zoomed page.

TODO: in reflow mode, study if pinch to zoom could affect images also.

[danielweck]

Related issue: #1825

[Mitia99]

@danielweck Any update on this ?

My issue is the viewer is too small when zoom is set on Fit and too big when set to 50%

Thanks for adding some priority on this,