Test+implement: object cache for email and domain.
Move the "dbObject"s to their own package.
There is a test case that needs cache punging.
UPD: cleanup notary-assurance API
Additional testcases for failing assurances.
UPD: Change the assurance API (and document it)

for cleaner race-condition checks in the future.
UPD: tighten Up the constructors of "User" and "Domain"
UPD: change "email"-constructor to match the syntax of the
domain-constructor.
UPD: fix "test assurance" to work with the strict caches
UPD: Clean Up "TestMyDetailsEdit" (by moving common code up)