To ensure easier development and maintenance, IE support is dropped to allow
modern Javascript features. The old tabber module is rewritten into newer
standard and using classes to ensure proper scoping.
It can be enabled by setting `$wgTabberNeueEnableLegacyMode` to `true`.
It is the first implementation and a WIP with numerous caveats:
- Nested Tabber does not work
- Tabber Transclue does not work