Moved the .png icons to `debian/hicolor-icons` and adjusted `debian/install`; thanks, @LocutusOfBorg!

Inside the `debian` directory there's a directory tree that's
supposed to be directly installed on `/usr/share/icons/hicolor/`.
Applied latest changes on `debian/changelog`
Updated .png icons path on `debian/source/include-binaries`
Added a Finnish GenericName to the desktop file, thanks to @jnumm