Bump SWE-GLib version requirement to 2.1.0

gswe_all_house_systems() was added in 2.1.0, which is required for
house system functionality.
Add house system node to example chart
Add the house system configuration widgets to the Edit tab

It is already filled with data, but it is not functional yet!
Add house system loading to chart load code
House system GtkComboBox now indicates the loaded house system
Now considering house system setting on the Edit tab
Merge pull request #37 from gergelypolonkai/configure-house-system

Make house system configurable