Moves the rule for requesting all states when no checkboxes are checked out of the server.

The rule is now applied in one place: in GetTransUnitActionContext.getCurrentFilterStates() (or rather in one of its helper methods).

NOTE: this pull request is purposely build on top of the Refactor FilterConstraints pull request ( https://github.com/zanata/zanata-server/pull/28 ) to see what happens when its base commits are merged.