Add PPLC (capitals) to cities.txt, and thus to geodata.xml
Redesign geodata.xml so it also stores country names
Add GtkListStore for city and country list
Create a DEFAULT_ALTITUDE macro

It is set to 280.0, which is roughly the average altitude of dry land
Bind signal callbacks with gtk_widget_class_bind_template_callback()
Fix ag_db_get_chart_data_by_id() to recognise NULL values
Read country/city list from geodata.xml into GtkListStores
Update UI to use country/city chooser
Empty/update city and country fields
Merge branch 'master' into city-chooser

Conflicts:
	src/ag-db.c
	src/ag-window.c
Merge branch 'master' into city-chooser
Merge branch 'master' into city-chooser
ag_window_recalculate_chart() now considers country and city names
Redraw chart when changing to the chart tab

Fixes #59
Force update of the focused widget on the Edit tab if it’s a GtkSpinButton

This is required because when the user changes tabs with an accel after
manually changing a spin button’s value, but without pressing Enter
("activate") or leaving the spin button, the spin button will reflect the
old value instead.
Country selection is now saved, so city list can be filtered
Merge branch 'master' into city-chooser
Merge branch 'master' into city-chooser
City changed code

This updates the coordinates on the Edit tab, too
Filtering city list based on selected country