proposal for checking for various situations of insufficient data

Hi @nicolashery. Sara seemed to have discovered a bug with rendering tideline once recently when she had no data uploaded but had one message coming through the API, and that got me to thinking about various situations of not completely missing, but *insufficient* data for tideline to render properly. I think these checks belong in blip, as they're rather app-specific, or at least especially the check for messages. I also added some code for tideline to fail loudly (in 6ec03111291be9499ceec6695cb478fcc1b97e63) in two of these situations, but IMO the checks (and subsequent `this.renderNoData()`) should be in blip as well. Let me know what you think.