Added some missing admin registrations.

[freakboy3742]

This adds admin registrations for Card and BitcoinReceiver (as inlines on Customer), and for TransferChargeFee (as an inline on Transfer).

This also enforced extra=0 and max_num=0 on inlines; this makes the admin representation much more terse (as there are no blank extra lines in the default rendering), and is as close as you can easily get to "readonly" (as you can't add new lines).

[coveralls]

Coverage remained the same at 100.0% when pulling ac4d7a6 on jambonsw:card-in-admin into aaa4516 on pinax:master.

[coveralls]

Coverage remained the same at 100.0% when pulling ac4d7a6 on jambonsw:card-in-admin into aaa4516 on pinax:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 46d158b on jambonsw:card-in-admin into aaa4516 on pinax:master.

[coveralls]

Coverage remained the same at 100.0% when pulling 46d158b on jambonsw:card-in-admin into aaa4516 on pinax:master.

[freakboy3742]

This patch includes the content of #297, as the test suite won't pass without it.

[coveralls]

Coverage remained the same at 100.0% when pulling 8aa80ac on jambonsw:card-in-admin into aaa4516 on pinax:master.

[paltman]

Thanks @freakboy3742!