Adding Role resource and RBAC grants

[donaldjarmstrong]

Resolves #87

Features:

• Added create role resource
  CREATE ROLE role_name
  UNIMPLEMENTED [ EXTERNALID external_id ]

• Added assignment of grant to role
  TO { username [ WITH GRANT OPTION ] | ROLE role_name | GROUP group_name | PUBLIC } [, ...]

• Added grant role to role or user
  GRANT { ROLE role_name } [, ...] TO { { user_name [ WITH ADMIN OPTION ] } | ROLE role_name }[, ...]
  UNIMPLEMENTED: [ WITH ADMIN OPTION ]

• Added grant role permissions

  {
    { CREATE USER | DROP USER | ALTER USER |
    CREATE SCHEMA | DROP SCHEMA |
    ALTER DEFAULT PRIVILEGES |
    CREATE TABLE | DROP TABLE | ALTER TABLE |
    CREATE OR REPLACE FUNCTION | CREATE OR REPLACE EXTERNAL FUNCTION |
    DROP FUNCTION |
    CREATE OR REPLACE PROCEDURE | DROP PROCEDURE |
    CREATE OR REPLACE VIEW | DROP VIEW |
    CREATE MODEL | DROP MODEL |
    CREATE DATASHARE | ALTER DATASHARE | DROP DATASHARE |
    CREATE LIBRARY | DROP LIBRARY |
    CREATE ROLE | DROP ROLE
    TRUNCATE TABLE
    VACUUM | ANALYZE | CANCEL }[, ...]
  }
  | { ALL [ PRIVILEGES ] }
TO { ROLE role_name } [, ...]

UNIMPLEMENTED: | { ALL [ PRIVILEGES ] }