MAINT: prepare for road test of adaptive algorithms

[stsievert]

What does this PR implement? It prepares for a road test of adaptive algorithm. Specifically, it does the following:

• [x] API: allow sampling algorithms with different frequency
• [x] MAINT: allow upload of ZIP files again (accidentally broken in #71).
• [x] MAINT, TST: better error handling of wrong parameters.
• [x] VIZ: adds visualization of response rate

Reference issues/PRs