ISIS-590: implemented.

Thus:
- if in Isis SERVER mode (= Wicket DEPLOYMENT mode), should strip wicket tags
- if in Isis PROTOTYPE mode (= Wicket DEVELOPMENT mode), should not strip wicket tags.

In both cases, can be overridden by setting "isis.viewer.wicket.stripWicketTags" config in one of the loaded configuration files (typically viewer_wicket.properties, but isis.properties would also work).

Have updated the example apps (for archetypes) also