Request - Edit: Prevent change of "Requesting Company" or implement ajax correctly

[alexander-spengler]

currently fields "Requester" and "Ship to" are wiped correctly, but "Receiver" is not

[alexander-spengler]

IMO should be prevented (to be consistent with other change restrictions; otherwise the change would lead to inconsistencies with data in related seed units and their events (change could be propagated to seed unit, but events cannot be reconstructed properly)

[feichler]

Request Edit: only allow to edit the number of requested units