Starting the ORM cache tool.

Getting a basic start on the ORM cache tool.
Add `orm_cache clear` command.
Extract helper method.
Add test skeleton for orm cache shell.
Add forceRefresh option to describe

This option lets you bypass cached data and always get fresh metadata.
Pass cacheMetadata option through to collection.

Without this the metadata cache will *always* use `_cake_model_` which
is not how the code should work.
Add mutator for cacheMetadata config.

I need to modify this config option during test cases, and I don't want
to allow all the config options to be mutable.
Get a few simple tests working.
Flesh out remaining tests for OrmCacheShell.
Small corrections

* Correct doc blocks for OrmCacheShell.
* Fix coding standards errors.
* Add missing default argument value.
* Fix indentation and failing tests.
Merge pull request #3536 from markstory/3.0-orm-cache-shell

3.0 orm cache shell