Changes

[509735] Fix two ActivityExplorerePage setters

The header title and page description setters did nothing. The effect
is not visible in the context of Capella:
* For "header title", concrete pages implementations are provided
  which override the getHeaderTitle() method.
* For "page description", it seems we always are in sub-classes of
  BasicSessionActivityExplorerPage, which overrides
  handleContributedSectionsFor() and does not use the broken
  "description" field from the page, but the one from the section
  instead.

Bug: 509735
Change-Id: I3e6f89422f021eb232c8e966f013d9c746f03da4
Signed-off-by: Pierre-Charles David <pierre-charles.david@obeo.fr>