Hide acceptable formats element on load

...because a disappearing blob looks weirder than an appearing one.

Auditors: eater
Adjust a conditionl.

Test plan: Open number_line multiple times in the athena branch and try dragging the point.

Auditors: alpert
Disable hint button after taking hints with reload

Auditors: alex, james
Only respect server side lastCountHints and lastAttmeptNumber if first page load.

Summary: People have said they have seen hints pre-filled in when it is not the first problem https://github.com/Khan/khan-exercises/issues/45794.  As both lastCountHints and lastAttemptNumber get set to 0 when problemDone is triggered and any out of date updateUserExercise should then get ignored in userExerciseCache _set. Hence I am not sure how this is happening, but hopefully this should fix it.  It should also make sure problems dont appear with hints filled in on the non-first problem loaded when in topic/mastery mode.

Test Plan: cross-fingers

Reviewers: alpert

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D2319

Auditors: alpert
Remove reference to non-existant "B" variable

Summary:
In the a-o-xmk and a-o-xmk2 answer-types of limits_2, there's a "B"
variable that isn't defined, but it renders fine without it (and the
question/answer still makes sense). So, if not running in debug mode,
the exception is caught and ignored, and the error goes unseen. This
removes all references to "B", which fixes everything.

Test Plan:
Visit
http://sandcastle.khanacademy.org/media/castles/xymostech:fix_limits_2/exercises/limits_2.html?debug&problem=a-o-xmk
and see that it doesn't break

Reviewers: alpert, eater

Reviewed By: alpert

Differential Revision: http://phabricator.khanacademy.org/D2344
Merge with stable master.