Check cancellation fee for own user

[eynimeni]

If an admin cancels a booking for himself the refund isn't calculated correctly.
e.g. courseprice is 80, cancellation fee is 5 but only 70 are refunded.
Also there is a problem with overwriting the cancellation fee. prices are not calculated correctly. it seems as if maybe the standard cancellation fee is added to the one entered in the field.
e.g. standard fee 5, fee entered in form 3, courseprice 80 -> 72 refunded