Add a summary/advice tab

[kog]

In addition to the summary of things like thread counts, sleeping threads etc., TDA shows a bunch of advice on the "dump node", the tree node corresponding to the highest level of the dump. This includes suggestions like:

• N% of your threads are sleeping, this might be resource contention or lots of waiting threads
• Warnings about monitors without locking threads

It would be worth seeing how hard this is to add

[kog]

Ran across a thread dump that caused me to file #3, which correspondingly would show up in the advice tab.