Touch control optimisation [iOS, Android]

[zverinapavel]

Added better touch controls for touch devices (iOS, Android).

One finger tap moves mouse cursor to the tapped position and does left mouse click. (new!)
One finger drag moves mouse cursor around. The finger doesn't have to be at the cursor position, but anywhere on the screen. This is useful for accurate selection of dialogue options, and precise aiming during combat.
Tap two fingers for right mouse click (switches mouse cursor mode).
Move two fingers to scroll current view (map view, worldmap view, inventory scrollers).
Tap with three fingers to simulate a left mouse button click at the cursor's current location without moving it. This is ideal for accurately selecting dialogue options or executing precise attacks during combat.

Also edited Readme.md with this explanation.

Fixes #180