make sending a confirmation email for requested evaluations to teachers optional

[irinahpe]

Evasys-managers can now choose wether to have an email sent to teachers of the course of which they started an evaluation on

[Laur0r]

Nice work, thanks! Only two small things, it would be good to have an additional help button explaining under what circumstances emails are sent to teachers (only when the evaluation is requested from the overview page). Second, for existing categories the checkbox is set to false not true, maybe you can have another look at that.

[irinahpe]

I added the help button and changed the default values also in the db-tables. But since the default values are saved as the persistent properties mode_flags in the evasys_category and the evasys_category is only created after the category has been added to evasys in the admin settings, it is not possible to change the dafault values afterwards.