Create a DEFAULT_ALTITUDE macro

It is set to 280.0, which is roughly the average altitude of dry land
Merge pull request #55 from gergelypolonkai/default-altitude

Create a DEFAULT_ALTITUDE macro
Bind signal callbacks with gtk_widget_class_bind_template_callback()
Merge pull request #56 from gergelypolonkai/use-template-callback

Bind signal callbacks with gtk_widget_class_bind_template_callback()
Switch to WebKit 4.0 API
Add an empty toolbar to the chart tab
Add connection view changer buttons (aspects/antiscia)
Merge pull request #57 from gergelypolonkai/chart-manipulation

Add chart toolbar with aspects/antiscia switcher buttons
Merge branch 'master' into city-chooser

Conflicts:
	src/ag-db.c
	src/ag-window.c