Adds the following methods for groups:

- index() - https://api.onthecity.org/docs/admin#groups_index
- show() - https://api.onthecity.org/docs/admin#groups_show
Merge pull request #1 from ericthelast/feature/add-group-methods

Adds the following methods for groups:
Adds show() methods to eventually replace get() methods.

This closer aligns the module with The City's api endpoints/methods.
Fixes syntax error.
Merge pull request #2 from ericthelast/feature/add-user-show-methods

Feature/add user show methods