Phase out hasClaim and newClaim

I focused on the deprecated methods hasClaim and newClaims in this
patch.

The idea is to make the strange patch
https://github.com/wmde/WikibaseDataModel/pull/280 smaller or at
least get rid of it faster.

Note that I still had to introduce more of these painful
new Statement( new Claim() ). There is no other way. If you see one
that does not make the test setup code explode, please show me.
Also see https://github.com/wmde/WikibaseDataModel/pull/268

Change-Id: I0777c53db88a90c34193545c439d5495fed4d6c6