rename and possibly refactor HtmlOptions

[ctm]

Rename types::HtmlOptions and possibly refactor its use.

HtmlOptions was initially part of the tournament_structure module, so it was (mostly) clear that it meant HTML options for a tournament structure. However, since I misjudged and wound up relocating it to types.rs, it now sounds more generic than it really is. StructureSheetHtmlOptions would be more precise, but I may be able to refactor it into a better place than types.

I'm running into this because the code for doing structure sheets is already fairly generic and could be extended to handle hand histories as well, but it does have some tournament-structure specifics, like HtmlOptions.

There are two different ways I can approach this. The quick fix is to add the StructureSheet prefix and implement hand histories independently of the existing tournament structure code, perhaps by trying to make the hand histories even more generic so that it can subsume the tournament structure code. The alternative would be to work directly with the existing tournament structure code (and rename it to be more generic) and then use the all-singing-all-dancing version to implement hand histories.

[ctm]

I've decided to do the rename as part of this ticket, but to explore the refactoring directly under (#576), since that already has some stub code that I'll want to take into consideration. So, I've done the rename and it's in master, but not deployed.