Updated Overlay to include constrain support, and renamed widget-position-ext to widget-position-align

Fixed overlay height/centering order. Fixes #2526042

Added Base.create and Base.mix sugar methods on top of Base.build (to mirror the common dynamic:true/false usage). Changed tablist sandbox and overlay to use them. README has details. Tested Overlay, Tooltip example, Widget Custom Class examples. Fixes #2528336

Code Review changes for Base: removed Base.create, removed support for dynamic:false, added name to signature

apidoc edits, no code changes

apidoc updates, plus minor code cleanup - renamed XXXX_CLASS static props to XXXX_CLASS_NAME [no upstream impact]

Code Review: Removed need for Widget.build. Just have Base.build, with config arguments defined as static properties on main class [low risk - currently only used by Overlay]

apidoc, initial stubs - module/class

Added HTML_PARSER to widget-stdmod

initial PR2 checkin for Overlay