XD-1645 Refactor Exception Handling and update JavaDocs

Also includes the XD-1466 to support the /management endpoint.

* All public ctors/methods must have Javadoc
* put no-arg ctors on the top of class file
* transient keyword removed.
* Checked exceptions replaced with unchecked.
* public method arguments are guarded with with Assert.notNull, Assert.hasText
* unecessary no-arg ctors removed
* getContainers replaced with getContainerUrls

* minor cleanup during PR review