disable pinch-to-zoom, drag-select-text for webxdc

[r10s]

pinch to zoom is more annoying than helpful in most games and apps, it should just be disabled for now; also android has it disabled.

doing a quick search, i found https://stackoverflow.com/questions/36581166/programatically-enable-disable-pinch-to-zoom-on-wkwebview-and-viewforzoominginsc , not totally sure if that's helpful.

moreover, playing eg. triska, one easily does a drag-select-text, resulting in the whole app getting a blue overlay ... also that should be checked, if it can be easily disabled.

[r10s]

for the text part, there seems to be textInteractionEnabled (came over that when checking https://github.com/deltachat/deltachat-ios/pull/1477 and found https://nemecek.be/blog/111/wkwebview-improvements-in-ios-15 )

[r10s]

usually, webxdc disable these things by <viewport> and related tags, to manage different defaults of different browsers. so, in practise, this is less of a problem.