API: Add timestamp of block to blockinfo

This change affects list=allusers, list=users
and meta=userinfo.

Note: This change also add block expiry to meta=userinfo.
Unlike this field in other modules, it formats the timestamp
properly, instead of just dumping db contents.

Resurrecting from abandoned change Ifdeac5c5f547

Bug: 63326
Change-Id: I4b3e55fe2d07271e1ded89d36d0b98de0e643177
Merge "API: Add timestamp of block to blockinfo"