Resolve "Integrate flask SSO panel into dashboard flask backend"

Closes #19 (closed)

This MR merges the Python code from the Single Sign On repository (the Login panel Flask application and the existing Python Dashboard Backend, so that we have a single Python back-end. It also contains very basic support for setting user roles. The only role you can set now is for the Dashboard application. The Dashboard application does not use the role yet.

Related MRs:

• dashboard!23 (merged) installs this code with an updated helm chart.
• stackspin!946 (merged) installs the updated helm chart and gets rid of the single-sign-on repository.