Models: Refactor some common code between tool shed and Galaxy into galaxy.model.orm.
Models: Refactor common code out between Galaxy and Tool Shed related to create_engine.
Models: Introduce real class for app.model (ModelMapping).

Shared across Tool Shed and Galaxy to reduce code duplication. Previously this was just a bunch, making it a real class allows placing some shared logic in there.

This refactoring also eliminates some global variables galaxy.model.mapping.Session, galaxy.model.mapping.context, and same for tool shed. This may break things, but these are things that should probably be fixed anyway.
Models: Random fixes for mapping tests.

PEP-8. Get rid of old test suite code mixed into real code.
Models: Unify 'now' import and comment across galaxy and toolshed.
Fix test suite for elimination of global variables related to ORM.

Essentially replace old references to global variables in Galaxy with references to global variables just defined in the test framework (a slight improvement).
Models: Move tool shed install related models and mapping into own package.

Specifically, refactor all tool shed installation related models and mapping information in Galaxy's models into new module galaxy.model.tool_shed_install.

This is work toward being able to store tool shed installation data into a second database. There is still a lot TODO, all access to these models are still through galaxy.model and the existing ModelMapping object, these references need to be refactored.

More information on the end goal here: http://dev.list.galaxyproject.org/Galaxy-less-Tool-Installing-tp4660655.html.