Add features to make overlay usable as a modal dialog

[mehaase]

The overlay already looks a bit like a modal dialog, but it lacks a built-in close widget. Ideally it would:

• Have an option to display a close widget.
• Have an option to close when the user presses the escape key.
• Have a way to wire a button inside the dialog to close the widget. For example, the caller may want to put a cancel button inside the dialog.

The first two could be the same option, i.e. [closable]='true'. The third item needs to be separate.

[mehaase]

Note to self: I have code to do the first two in a private project. The third item will require some Angular black magic.