Optimise application list generation

Places where the list of applications is generated, i.e. the job offer page and export applications button, currently take too long to load. Temporarily, the 'took course' information has been disabled, but 'TAed before' also takes a long time to load. This information should be requested before in one go, instead of once per row.

For this issue

• Move all the data retrieval to happen in one go at the start of the request
• Re-enable the 'took course' functionality