Added mechanism to allow subclass to veto the adding of classes to the application context; controlling what classes are available to the user.
Added mechanism to allow subclass to veto the adding of classes to the application context; controlling what classes are available to the user.

git-svn-id: 3f09329b2f6451ddff3637e937fd5de689f72c1f@1007557 13f79535-47bb-0310-9956-ffa450edef68

howepeng/isis,sanderginn/isis,niv0/isis,apache/isis,incodehq/isis,sanderginn/isis,peridotperiod/isis,niv0/isis,niv0/isis,apache/isis,incodehq/isis,oscarbou/isis,apache/isis,sanderginn/isis,apache/isis,sanderginn/isis,incodehq/isis,estatio/isis,howepeng/isis,incodehq/isis,apache/isis,kidaa/isis,estatio/isis,peridotperiod/isis,apache/isis,oscarbou/isis,peridotperiod/isis,peridotperiod/isis,howepeng/isis,oscarbou/isis,estatio/isis,kidaa/isis,oscarbou/isis,kidaa/isis,howepeng/isis,kidaa/isis,estatio/isis,niv0/isis