Remove TODOs

There's a bunch of TODOs in code now. We previously had them all removed, in favor of creating tickets to track work. I guess we've been less rigorous about that recently.

All the existing TODOs should be checked for relevancy and deleted. If they are still relevant and an issue does not yet exist for them, then the details should be put into a new issue for proper tracking.

I understand that the "TODO" keyword may be helpful in some IDEs that report such things, but it does more harm than help to have issues tracked in multiple places, and here is where the project has decided to track issues, because we can't make reliable assumptions about what IDE (if any) a contributor might be using. Some IDEs have plugins that allow them to show issues (Eclipse has Mylyn, for example) if one wishes to see them in their IDE.