Refactor all module Toolbar Buttons by Merge into one PNG file

We can merge all 135 "tool_*.gif" files of Core module into singe
file. We could do the same for all other modules as well, so we end up with
1 file per module, that will contain all toolbar images.

This approach allows to save page load time. Also we will add css classes,
that will contain position of each toolbar button in the file.

Toolbar buttons will be located in file like this:
[Add Button Enabled] [Add Button Hover] [Add Button Disabled]
[Modify Button Enabled] [Modify Button Hover] [Modify Button Disabled]