Get rid of settings in ModifyClaim

Change-Id: I6d6a6bd7a398c8b592e2520461d49e82f625dc04
Rename ChangeOpClaim to ChangeOpMainSnak

- as suggested by DanielK
- is a more suitable name

Change-Id: I5bbbfc408569733897e2a35fbe84426d2d0e95b3
Move snakValidation to ClaimModificationHelper

Change-Id: I80e1489a28cff5f078126b7fd55c4d6400d47221
Merge changes I80e1489a,I5bbbfc40,I6d6a6bd7

* changes:
  Move snakValidation to ClaimModificationHelper
  Rename ChangeOpClaim to ChangeOpMainSnak
  Get rid of settings in ModifyClaim