Context pages: show project name as additional information.

Summary:
The lambda is the same as in WorkdayPageModel, but well it's just
9 lines of code (and maybe we want to show contexts in the workday page
later).

Test Plan:
Context pages now show project names.
This allows to write task description with less redundancy...

Reviewers: ervin

Reviewed By: ervin

Subscribers: Zanshin

Differential Revision: https://phabricator.kde.org/D16510