Add optional yalign argument to Utils::mk_label() method

As part of the work on bug 652044 - uses deprecated APIs, selectable
vertical alignment was defaulted to ALIGN_CENTER for all labels.  The
relevant commits can be viewed in comment 26 of said bug report.
https://bugzilla.gnome.org/show_bug.cgi?id=652044#c26

For multi-line labels a vertical ALIGN_CENTER value is not
consistently aesthetically pleasing.  This becomes obvious when a
single-line heading label is paired with a multi-line value label.
To improve the aesthetics, a vertical alignment of ALIGN_TOP is
preferred.

Hence re-add the ability to optionally specify a vertical alignment for
labels.  If a yalign value is not specified a default vertical alignment
of ALIGN_CENTER is used.

include/Utils.h

@@ -162,6 +162,7 @@ public:
 	                            , bool use_markup = true
 	                            , bool wrap = false
 	                            , bool selectable = false
+	                            , float yalign = 0.5 /* ALIGN_CENTER */
 	                            ) ;
 	static Glib::ustring num_to_str( Sector number ) ;
 	static Glib::ustring get_color( FILESYSTEM filesystem ) ;

src/Utils.cc

@@ -46,12 +46,15 @@ Gtk::Label * Utils::mk_label( const Glib::ustring & text
                             , bool use_markup
                             , bool wrap
                             , bool selectable
+                            , float yalign
                             )
 {
 	//xalign 0.0 == Gtk::ALIGN_LEFT  (gtkmm <= 2.22)
 	//           == Gtk::ALIGN_START (gtkmm >= 2.24)
 	//yalign 0.5 == Gtk::ALIGN_CENTER
-	Gtk::Label * label = manage( new Gtk::Label( text, 0.0, 0.5 ) ) ;
+	//       0.0 == Gtk::ALIGN_TOP   (gtkmm <= 2.22)
+	//              Gtk::ALIGN_START (gtkmm >= 2.24)
+	Gtk::Label * label = manage( new Gtk::Label( text, 0.0, yalign ) ) ;
 
 	label ->set_use_markup( use_markup ) ;
 	label ->set_line_wrap( wrap ) ;