Add support for API Keys

[nwmac]

At present, the backend API only supports auth via an interactive user session - the user must login via the UI and have a valid session cookie.

There are several use cases that would be helped by allowing users to create API Keys, much like many other systems, such as GitHub.

• Add a table to the db to store API Keys, these should be bound to a given userid
• Add middleware to the backend echo router that detects if there is no session but an Authorization header is present and then validates the API Key and creates a session for the duration of the API Call, so that it can proceed
• Add Rest API for creating, listing and deleting API keys - the API Key should only be returned once with the creation API

The main parts of the Stratos API that we want to expose are:

• Adding, deleting, updating and listing endpoints
• Adding, deleting, updating and listing tokens