Remove unused Catalog.get_image_coordinates()
Remove unit test for Catalog.get_image_coordinates()
Add missing LEMON icon

This should have been included in commit 03dd47a6.
Remove hard-coded version number from the GUI window title
Add coordinate_query() module-level function
Add 'Look up in SIMBAD' button

Use a stock button, STOCK_INFO, but with a different label, 'Look up
in SIMBAD', by getting the label child and setting the text directly.
The button is not yet functional
StarDetailsGUI.__init__(): store α and δ as attributes
Add StarDetailsGUI.handle_look_up_in_simbad()
Connect 'Look up in SIMBAD' button to its handler
Add LEMONJuicerGUI.handle_look_up_in_simbad_accelerator()
Set <Control>S as the accelerator
Factor out duplicate code into _activate_StarDetailsGUI_button()
Merge branch 'add-look-up-in-SIMBAD-button'