Fix bug that could cause segfault when there are odd number of display themes
Move country/city set calls before longitude/latitude set calls

Changing the country and city values trigger the callback that
automatically sets the coordinates based on the city name. Thus, values
possibly entered after changing the city may update the already entered
values. The same problem occurs when a new chart is loaded with correct
coordinates but incorrect city name.
Add new built-in theme "No comets"

This theme displays all aspects and antiscia, but only planets. No comets
and dwarves are displayed.