Give Conduit params/return/errors protected visibility

Summary:
Ref T7803. Ref T5873. I want to drive Conduit through more shared infrastructure, but can't currently add parameters automatically.

Put a getX() around the defineX() methods so the parent can provide default behaviors.

Also like 60% of methods don't define any special error types; don't require them to implement this method. I want to move away from this in general.

Test Plan:

• Ran arc unit --everything.
• Called conduit.query.
• Browsed Conduit UI.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: hach-que, epriestley

Maniphest Tasks: T5873, T7803

Differential Revision: https://secure.phabricator.com/D12380