Clean up and polish Mifare Classic tech.

- It's useful to have accessors at block level, so apps don't really have to know
  about the sector structure (and how many blocks there are in a sector).
- There's no way to tell whether a read/write/ didn't work because of auth
  failure. The documentation should be changed to make this point clear.
- Added increment/decrement commands, for atomic increment/decrement of value blocks.

Change-Id: I590feacbcd1443f1be7a86ab046a5b1f33e2e04c