added support for tile size for game elements info screen

This adds support for the following two graphics configuration options
to customize the element tile size and the space between element
graphic and element description on the game elements info screen:

* menu.tile_size.INFO[ELEMENTS]      - tile size of element graphics
* menu.middle_spacing.INFO[ELEMENTS] - space between element and text

Supported tile sizes are game tile size as defined by "game.tile_size"
and the usual standard tile sizes 32, 16, 8 and 4 pixels.