[GTK,WPF] ListViewColumn: add support to set the alignment of the title
Extend color selector example
[GTK] add color selector backend
fix HSL conversion in DefaultColorSelectorBackend
extend DefaultColorSelectorBackend
* replace text entries with spin buttons
* add opacity slider
[GTK] use system default title in SelectColorDialog, if no title is specified
Merge branch 'master' into listviewcolumn-alignment
[WPF] Util: keep the original formatting
[WPF] Util: fix line endings
[MAC] fix toggle button
 * add OnToggled event
 * use NSButtonType.PushOnPushOff
extend button sample with some ToggleButton toggle actions
[MAC] mark ButtonBackend.SetButtonStyle as virtual
(was missing in @2070102)
fix typo in button sample
Merge remote-tracking branch 'mono/master' into add-color-selector-backends

Conflicts:
	Xwt.Gtk/Xwt.Gtk.csproj
[Xwt.Wpf] Add ComboBox support to PlaceholderTextAdorner

We also have cases where comboboxes need to be adorned with
placeholder text.
add TextEntry.PlaceholderText samples with different alignments
[WPF] fix PlaceholderText alignment and initialization
[GTK2] convert RenderPlaceholderText to an extension method
and move it to Gtk2Extensions
[GTK2] add Gtk.Widget.RenderPlaceholderText_internal
extension method for easier implementations for
other editable widgets.
[GTK2] fix TextEntry.PlaceholderText positioning
for different alignments