API Database refactored into controller/schema/connector components. Ticket #7429

Created new framework based on main database class, with separate classes to handle connection and schema management
Refactored database into base database class, connector class, schema manager class, and query class. These are hooked together via dependency injection with database recipes handled via yaml / Config subsystem.
New syntax for beginSchemaUpdate. Now schemaUpdate wraps a callback.
Updated phpdoc
Retired many instances of incomplete and legacy database code
New standard implementation of requireIndex and updated convention for handling of index specification strings. This should prevent having lots of is_array conditions during schema updates.
Added new PDOConnector and set as the default MySQL connector class.

Prepared statements not implemented yet.