DeleteView doesn't work for projects which don't use TempEntityClass

[koeaw]

Issue for WIP PR #458.

Describe the bug
As I started to work on #437, I noticed I couldn't get GenericEntitiesDeleteView to work at all because it still refers to TempEntityClass.

Once I'd fixed that, the confirmation template for deletion, which is not entity-specific but shared between views, wouldn't show me any information on what exactly I was deleting.

While looking at the HTML, I also noticed that it was generally off in places, e.g. buttons which belong together don't sit next to each other for some reason, convoluted wording for the "Cancel" button, a nonfunctional close button,...

[koeaw]

We agreed to split this in two to reduce complexity:

• the first/existing PR should solve the faulty model reference in the view and (if applicable) fix the reference to the entity in the template
• the other issues with the template (formatting, styling, tweaking of information displayed to users,...) should go into a second, independent PR

[b1rger]

Not exactly sure which of the two parts this issue relates to- according to the title probably the first. This would be great to have soon, as deleting an instance is a rather important feature (and its a small fix)

[koeaw]

Ah, right! Thx for the reminder.

I'll reduce #458 down to what's needed to fix the first obstacle (TempEntityClass).