Support multiple quizzes for a single CME front-matter

Required for Rap. This significantly alters the database design and all the pages, tools and admin components. Some vocabulary is updated to match reality.

See https://docs.google.com/a/silverorange.com/drawings/d/1XfdUBOcMju1xudWNFsrDqzf-hCm7fmCgmrC2SmrpMRY/edit for the new database diagram.

 * CMECreditType becomes CMEProvider
 * CMECredit becomes CMEFrontMatter
 * CMEFrontMatter contains an evaluation and the attestation content
 * CMECredit is a new object with hours and a quiz. CME-specific quiz features are also moved to this table instead of the Inquisition table
 * AccountEarnedCMECredit is a new binding for earned credits so we don't always have to query an entire quiz response to display earned CME credits
 * AccountCMECreditBinding becomes the more descriptive AccountAttestedCMEFrontMatter and an attested_date is added

Requires silverorange/Inquisition#9
If there is only one available provider, we should drop set `$provider_widget->show_blank = false;` which would make users make one less selection.