Slider: use standard attribute for specifying position of children

[bill]

Current API for specifying layout position is OK:

<div dojoType="dijit.form.HorizontalRule" container="topDecoration" ...></div>

But the problem is implementation. Can't create slider programatically:

new dijit.form.HorizontalRule({container: "topDecoration", ...});

Probably can be solved by removing custom code from _Templated to handle container flag and instead just do something like this in postCreate():

dojo.forEach(this.getChildren(), function(child){
 this[child.container].appendChild(child.domNode);
});

[Douglas Hays]

(In [9574]) Fixes #3686. Removed child.container processing from _Templated.js and added startup() to Slider.js to handle children placed within the wrong decoration container.

[bill]

(In [9632]) Revert [9629]. It broke many of the widget tests including test_Button.html. "" is not an invalid value. Also need to print the widget's id or at least declaredClass. Reopens and refs #3686.

[bill]

Ignore the above two comments, which obviously refer to a different bug (but I don't know what #)

[Douglas Hays]

I thought this was fixed in [9574].

[bill]

Note to self: I confused this bug with #3700. This bug is indeed fixed.