osc: Once again new Show/Hide handling

The deadzone-size is now by default zero, so movement on the entire window will make the OSC show up. To avoid it showing up by randomly moving mice, the option 'minmousemove' controls how many pixels movement (default: 1) between ticks (frames) are necessary to make the OSC show up.
The deadzone can be reenabeled by setting the option 'deadzonesize' (default: 0 = no deadzone, 1 = entire area between OSC and opposite window border), to restore the old behavior, set it to ~0.92.

The OSC will hide immediately when leaving the window or entering the deadzone (if existing) or after the time specified with 'hidetimeout' (default: 500ms) passed without any new movement. Set to negative value to disabling auto-hide (thus restoring old behavior). The OSC will never hide if hovered by the mouse.