webadmin,userportal: Support tab index handling in dialogs

This patch adds the necessary infrastructure to support tab
index handling consistently across all application dialogs.

In general, tab index values are updated for both dialog content
(i.e. widgets contained within popup view directly -or- widgets
contained within popup view's content widget [1]) and dialog
footer buttons.

Tab index values are updated on following occasions:
(a) right before the dialog gets revealed in UI,
    i.e. right after view.edit (before popup reveal)
(b) when dialog footer button collection is modified,
    i.e. right after new button gets added via model
(c) upon stopProgress, right before calling focusInput

In other words, after this patch, the only thing a dialog class
(AbstractModelBoundPopupView subclass -or- content widget [1])
needs to do is to override setTabIndexes method.

[1] AbstractModelBoundWidgetPopupView.popupWidget

Change-Id: I8b5c7d6a9e7b98c1f5e1fecbaaf193cd862ccb47
Bug-Url: https://bugzilla.redhat.com/1011445
Signed-off-by: Yaniv Bronhaim <ybronhei@redhat.com>
Signed-off-by: Ravi Nori <rnori@redhat.com>
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>