Bug fix and code cleanup in form widget:

1. Cache keys must include delegator name. Multiple forms based on the same entity name might be completely different due to the delegator being used.

2. Do not hold references to ModelReader and DispatchContext after construction.

git-svn-id: https://svn.apache.org/repos/asf/ofbiz/trunk@1636158 13f79535-47bb-0310-9956-ffa450edef68