HeaderLabel: wrap title, halign FILL

[danirabbit]

Having this set to halign = START by default ends up with us overriding this in a bunch of places. All other widgets default to FILL

wrap the title while we're here

[ryonakano]

Maybe we need to update the documentation comment here?

/**
 * HeaderLabel is a start-aligned {@link Gtk.Label} with the Granite H4 style class
 */
public class Granite.HeaderLabel : Gtk.Widget {

[danirabbit]

@ryonakano updated! The label itself is still start aligned so I left that bit in