Added moving selected items

Click and drag on a selected item to move it. If multiple items are selected, continue to hold shift for the initial click of the drag otherwise it will deselect the group and only select the item clicked on for the drag. You might as well hold shift for the whole drag/moving operation.

Currently it's on a 50ms timer as opposed to the 100ms timer of drawing paths. This might need to be changed when considering performance of the server.

This addresses issue #68.

I don't know what happens if two people try to move the same object at the same time. Need to implement a server-side token mechanism to give movement access to whoever clicks first.