Modify Bean Tree and Detail views to allow independent scrolling

[phantomjinx]

See #593 for details.

Summary

The Bean Tree and Detail views are both drawn inside the same scrollable container meaning that when scrolling down the former, the latter is also scrolled. Add a scrollbar to the Bean Tree that works independently of the Detail View.

[phantomjinx]

Copied to hawtio/hawtio-next#1380