Expose UI for collecting IO traces

http://svn.apache.org/viewvc?view=revision&revision=1827841 introduced utility classes to collect IO traces. See e.g. https://issues.apache.org/jira/browse/OAK-5655?focusedCommentId=16415730&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-16415730. Currently the only way to run such traces is via code or JUnit (see IOTracerRunner).

Going forward we should wire this functionality to oak-run to make it more generally useful.

frm, FYI.