MDL-45054 Conditional availability: HTML structure improvements

1. Changed the 'delete' and 'eye' buttons to use an <a> link
tag so that it works without custom tabindex and shows a correct
mouse cursor. This also reduces the code slightly.

2. Changed the Cancel button on the dialog to use the mdl-align
class which is used in Atto dialogs. This results in the button
being centered, consistent with those dialogs.