Introduce Styling Mods

Spotfire design can by quite nicely twisted with CSS stylesheets and similar approaches, but Spotfire 'themes' are a bit limited in variety. Also it does not fit into the community idea of Spotfire Mods.

The idea is to have "styling Mods" - from a flyout the user can drag&drop the style to either the complete tab or to single visualizations. So it's not only CSS style sheets being applicable with one click, also it is easy to make the settings of individual visualizations re-usable easily.

For the latter, there could be the other way back: simply drag an existing visualization onto a special area of the Style flyout and give it a name - creates a new Style setting. As some of the settings can be shared between different visuals, this would also provide the possibility to copy e.g. colour ranges, font sizes and similar.