MT#4145 Change postcode to txt, fix empty reseller

Postcodes can be alphanumeric in certain countries.

Avoid fault when editing a contact without reseller
(e.g. reseller/peer contact). You still can't save it without
setting a reseller (which might not be what we want).
MT#4237 Fix create of reseller on billprof edit

The field handler for the reseller button was missing in the
billing controller edit function.
MT#4317 fraud limits: fix labelling

seems to be in cents instead of Euros,
also add the label where it had been missing
MT#3855 Fix empty contract tab on Reseller details

When the reseller has a wrong contract assigned to
him, this contract is not shown because it has already
been filtered out in the Contract controller. In favor
of usability now show it anyway.

Also only present correct contracts on edit/create
resellers in the first place.

See (Mantis:3855#c25797)
MT#4609 extend checks when editing the own admin user to prevent locking oneself out