Open-event-server: Show actually paid ticket price in view Attendees section

[mariobehling]

The view attendees section of event organizers has a column with the ticket price. Please show the real price paid here (e.g. if people are using discounts) instead of the normal ticket price.

[PARAG00991]

I'd like to work on this issue.

[niranjan94]

@PARAG00991 you can proceed working on this once you're done with #2877

[magdalenesuo]

I'm doing 2878 and this is also fixed by a similar change, I'd like to do this aswell and fix this in the same PR...

[SaptakS]

@magdalenesuo @niranjan94 I think there is a ambiguity we should clear first about this 2 issues:
https://github.com/fossasia/open-event-orga-server/issues/2878#issuecomment-271377070

After that @magdalenesuo feel free to work. Since you are working on #2878 the same code should fix both the issues.

[mariobehling]

I think the questions have been cleared up. Please proceed. Cheers.