Add getFrom and setIn methods to Property for accessing object state via reflection; Implement equals and hashCode

Tweak the behavior of PropertyUtils.setProperty to match the behavior of PropertyUtils.getProperty when
nulls are encountered along a nested path - now the exception behavior is symmetric.

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1531989 13f79535-47bb-0310-9956-ffa450edef68