Minor improvements

This week I added option to modify brush and pen of selected element. I also added support for delete operation of the same element on both sides and combination of delete and update. I had a problems with bug which caused weird behaviour when I repeated several times delete and update operations of the same element, but I fixed that already and everything is working fine now as you can see here: http://www.youtube.com/watch?v=0_dta0JjPlI . I still need to implement moving of elements up and down and add some small fixes but whiteboard is almost ready.