[RFC] Simplifying the mapper layer

[adamlundrigan]

The AbstractDbMapper provided by ZfcBase, and by extension ZfcUser's UserMapper, duplicate a ton of work that can easily be handed off to ZF2's built-in TableGateway system.

• Building and executing SQL queries
• Hydrating result of select() calls
• Master/Slave adapter support

Utilizing TableGateway would strip ZfcUser's mapper down from ~400 lines (including AbstractDbMapper) to ~125 and remove the hard dependency on ZfcBase\Mapper\AbstractDbMapper, leaving ZfcUser's mapper as a just a thin wrapper around TableGateway that provides convenience methods (findBy*) and extracts entities passed to insert/update/delete methods.

An initial prototype of the refactoring can be diffed here. The modifications build on the result of #554, so I will submit a PR for this changeset once that PR has been completed.

[adamlundrigan]

One issue I've had with the previous mapper is with custom queries on the user table. AbstractDbMapper exposes getAdapter so you could do queries directly against that, but I found it better to just extend the mapper class and add a custom method for my query...which works fine until you get two modules that want a custom query each.

IMO the most straightforward solution would be to expose the TableGateway's selectWith method, though I'm not a fan of the encapsulation leak of having to know the database column names to build the query.