toolbar: Destroy the window on close if GTK+ version is older than 3.9

gtk_window_close was introduced in 3.9.
window: Hide titlebar when maximized if GTK+ version is older than 3.9

We can't set a custom titlebar before 3.9, so hide the titlebar from the window
manager when maximized.
Pass an empty string as illegal characters for unescaping

This is for backwards compatibility with GLib <= 2.36
toolbar: Hide close button if not maximized and header bar is not title bar

If GTK+ version is older than 3.9 which allows custom title bars, show the
close button of the header bar if we are maximized and selection mode is not
enabled.
grilo: Add missing parameters to _on_source_removed