Updating compatibility for Hydra 1.1

[JackUrb]

Overview

Hydra 1.1 introduces some breaking changes alongside really desired functionality, so this PR includes changes to get us up to the new standards.

Resolves #488

Details

Migrating config folders

By default, hydra used to use the local directory as the source for finding config paths. Now this behavior is deprecated, and we need to provide a source directory. As an upside, this also means we can eventually collect a repository of common configuration options in the future.

This updates all of the demos to pull from hydra_configs now.

Migrating groups

Hydra used to configure groups with directive keywords, but now the default behavior for a package with a given name is to automatically expand _group_._package_, which means we can simply specify the name and group and not need to add the package when we're registering a config.

Default merging

By providing default values in the base MephistoConfig for blueprint, provider, and architect, we were confusing Hydra's automated merging. These aren't really necessary, and so I've replaced with MISSING.

Testing

Ran all of the examples locally, ran unit testing.