Adding TODO about future refactor of Mode

Test Plan: Crossed fingers

Reviewers: alpert

Differential Revision: http://phabricator.khanacademy.org/D1006
Nicer warning/explanation about need for threading support for sampling profiler
Nicer firefox scrolling behavior when lots of ajax requests are fired
Get rid of browser prefixes for border-radius CSS
TODO and more explanatory comments
Add comment clarifying source of _current_frames suggestion
Cleanup should_sample logic that differentiates b/w dev and prod environments. Also add more explanatory comments.
Get rid of out-of-date comment about appstats locking
More explanatory comments about hack for identifying threads on the dev server for the sampling profiler