Add a pretty string formatter for boolean expressions.

The function builds a human readable string out of the content of the
expression. The main purpose is to ease the debugging of these functions.
The mouse buttons are ignored on Android builds.

The goal is to avoid being notified of both the finger and mouse events when the
user touches the screen.
Code clean up.

Moves the process of triggering the toggle in a separate function.
System toggles reacts to the fingers on pressure only.