adding a .LRN context bar that aids navigation on pages within applications mounted under classes and communities. TODO: provide the context bar also for application under the main dotlrn instance at /dotlrn (My Files, My Calendar etc.). This commit largely fixes bug 391.
changing presentation of current user name in master template. The name now simply appears in the upper right corner. Deciding after feedback from Lars and Carl to not to reuse the box from OpenACS as it duplicates links in .LRN and doesn't fit in with the design.