Adds roles for varied access

[hpjaj]

Description of changes

Creates a Role table giving certain users the ability to have varied access. This is accomplished in conjunction with Pundit.

Todo

• [x] update user serializer to include a user's role

Issue Resolved

Fixes #289

[apex-omontgomery]

Could this be a good way to add a role for the slack bot?

[hpjaj]

No, but good thinking. We're going to need to be more secure than that. We'll be going through more of a token based authentication process.