[WPF] Add support for alert dialogs with custom buttons
Improve size calculation in Box

When calculating the size of a Box and one of the size dimensions is
constrained, use that constraint to calculate the size of the other
dimension.
[WPF] Better spacing for command buttons
[WPF] Fix Label wrapping issue
[WPF] Fix sizing issue

It is not necessary to explicitly set the size of a widget when the
a size request is set. The Widget class takes care of it.