Implemented index parameter in ChangeOpClaim

(requires change Iefeebdcc4c6bc8c477d3f234399bcd403466bd52)
The optional index parameter determines the position of a claim within the subset of claims
whose main snak features the same property.

Change-Id: I53c98c09c96ce21e261e2fc1f02558eae31b568b
Merge "Implemented index parameter in ChangeOpClaim"