Add new image access method using filenames instead of hard-coded IDs.
Convert reticule GUI code to use this new method.
qtscript: Add setReticuleButton(id, tip, filename, filenameDown) to define the look of reticule UI buttons.
qtscript: Add two new functions: showInterface() and hideInterface(). They currently
only serve to assist modifications of the reticule, but will eventually control
hide/show of the larger user interface widgets. Also fix alpha values on two reticule
images.