CAY-1831  CayenneRuntime.getContext - replace with newContext

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1486469 13f79535-47bb-0310-9956-ffa450edef68
CAY-1831  CayenneRuntime.getContext - replace with newContext

docs update

git-svn-id: https://svn.apache.org/repos/asf/cayenne/main/trunk@1486470 13f79535-47bb-0310-9956-ffa450edef68