Allow disabling double tap behaviour

[TzwennD]

Add TextSwitch in Preferences to allow disabling centering
at double tap.
This centering can be quit annoying especially when looking up
a location far away.

[otsaloma]

I have noticed the annoyance of accidental double-tap, but adding a preference is, as usual, a bit of a weasel-solution. I have considered adopting the more common way of zooming in on double-tap and adding a button in the map view for centering. But, that's still undecided. I'll keep this open for now and either merge or reject depending on when or if I have a better fix.

And, ignore the failing CI, it looks like Mapzen's servers are finally failing.

[otsaloma]

I have considered adopting the more common way of zooming in on double-tap and adding a button in the map view for centering.

Done in WhoGo Maps. I might not change this in Poor Maps anymore, but if I will, I'll copy the change from WhoGo Maps.