Using module's images instead of the system ones

At the moment, images shipped with this module are not used, and the module is trying to fetch system images for collapsing/expanding the menus.

This is not the most optimal solution as it does not work in different setups (e.g. if this module is shipped with an installation profile, or is placed in sites/all/modules/contrib folder).
Right now it causes a 404 Page Not Found error, because the current paths to images are not correct.

Attached patch uses images shipped already with this module. This will work wherever the module is placed.
It also includes code formatting.

Let me know if any questions - thanks!