Generics changes for o.a.t.util.modeler

Generics changes for o.a.t.util.modeler
These changes identified a bunch of issues, the most serious of which was the loadDescriptors() method that sometimes returned List<ObjectName> and sometimes List<ManagedBean>. Some callers expected this, some didn't.
There are comments in the code identifying this as an issue. The fix I applied aligns with some commented out code that may have been part of an intended fix. There are still some deprecated methods that need to be cleaned up.
With these changes Tomcat starts without error and JConsole shows all the mbeans I expect to see.
There is plenty of further clean-up required here but I'll do that separately after the generics.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@718452 13f79535-47bb-0310-9956-ffa450edef68