Add System Services to Sandbox SDK

Add new scopes for key services in the Sandbox SDK:

• Items
• Collections
• Fields
• Relations
• Files
• Users
• Roles
• Permissions
• Policies (v11)

Support only multiple methods (readItems, createUsers, etc) and not singular methods (readItem, createUser).

Use the syntax in the public JS SDK and not the existing extension SDK (tradeoff decision between new extensions and migrating existing ones). Must support the same query object syntax as the JS SDK.