Removing dead code
Updated integration test for input()
Implemented ContextInterface::isPrimary, this helps deciding whether
a field is primary in a multi-record form or when dealing with
associations
Added test for ArrayContext::isPrimaryKey()
Adding test for
Adding test for EntityContext::isPrimaryKey
Fixing NullContext
Merge pull request #2917 from cakephp/3.0-more-formhelper-pt2

3.0 - adding isPrimaryKey to form Context classes