Deep nesting of DOM elements for effect UI

[dronus]

The UI's effect blocks are build by a quite complex DOM. Can we clean this up?

• UI build trees from div.ui_number, div.ui_string or div.ui_object. Those are filled with spans span.key followed by span.value, which may be filled by plain data or another div.ui_object, if the datatype sports a subtree
• Every effect contains an ui_object at the top level, featuring an empty key span and a value span wrapping everything. Is this two-level top wrapping needed?
• The intertweened span.key and span.value seem useful, as they provide easy style and easy access to key and values in the code.
• It's hard, despite useful, to use a key in the CSS, as it is stored as HTML text in a span.key followed by the target span.value field. As CSS sports no parent-selectors nor text-dependend selectors, one can not select span.value or div.ui_... elements sporting a certain key. This seems not to be easily solvable.

[dronus]

Unneded top-level containers addressed by #16.