Allow selection of template

[tobiasreischmann]

To prepare a lecture for evaluation, all courses have first to be synced to the evasys system. This is usually done by the evasys admin. Afterwards, the persons responsible for the evaluation create the evaluations for each course based on some template. In future, the templates could be also selectable for the teachers. For this, it should be possible to specify the set of available templates based on course category (or each course category for which a responsible person is defined).