Update big blind ante code and documentation

[ctm]

Allow the big blind to be paid before the big blind ante, and make that be the default.

See tzs4z's PR that covers what has changed and then make it so that mb2 can do it the "new" way. If it's easy enough to make it an option, continue supporting the old way and then make sure that all the past tournaments that used the old way are flagged as such. OTOH, if that is too much of a PITA, just go ahead and only support the new way.

In addition to changing the code, make sure that templates and structure sheets specify the specifics and also change the Players' Manual, if the old way is currently documented. If it's not already mentioned, no need to change the Players' Manual, since that's a bit stale these days anyway.

I've labeled this as high priority, but I doubt it matters much before EMBARGO.