Add configuration option for disabling mouse warping

This patch adds a new configuration option "mouse_warping [output|none]".

When mouse warping is disabled, mouse cursor does not jump to middle of current
screen when changing workspaces between multiple outputs. This introduces a
"special" cursor state, where focus is in one window and cursor on another.
Useful for eg. scrolling a web page with mouse wheel while typing into another
window on keyboard.

include/config.h

@@ -109,6 +109,16 @@ struct Config {
      * It is not planned to add any different focus models. */
     bool disable_focus_follows_mouse;
 
+    /** By default, when switching focus to a window on a different output
+     * (e.g. focusing a window on workspace 3 on output VGA-1, coming from
+     * workspace 2 on LVDS-1), the mouse cursor is warped to the center of
+     * that window.
+     *
+     * With the mouse_warping option, you can control when the mouse cursor
+     * should be warped. "none" disables warping entirely, whereas "output"
+     * is the default behavior described above. */
+    warping_t mouse_warping;
+
     /** Remove borders if they are adjacent to the screen edge.
      * This is useful if you are reaching scrollbar on the edge of the
      * screen or do not want to waste a single pixel of displayspace.