fix#626 (editor expander bug)

less intrusive method to fix #626 compared to solution of #671.
the #671 solution modifies the modal plugin, this not. Ie, will not cause problems when upgrading to the new version modal plugin.
So i will close #671.

Problem occurred (conflict with modal and sceditor) because sceditor use zindex 3 and modal use zindex 2.
I increase value of zindex of modal.
And removed comment in position: relative; to solve problem with editor expander bug.