Merge pull request #59 from PrivateStorageio/56.zkap-count-web-interface

Add a web interface for retrieving the number of unblinded tokens remaining.

Unblinded tokens have a one-to-one correspondence with ZKAPs.  That is, the number of ZKAPs
remaining is equal to the number of unblinded tokens remaining.  ZKAPs are created at the point
of use, though, so they cannot be counted/listed/exported/etc directly.