Improve flexibility of database related settings and bug fixes

The database related settings (mysql & mongodb) were set in one big dictionary variable containing all the parameters:

• some are secret like passwords and some aren't,
• some change at each deployment like host names and some never change.

In Arnold, credentials are stored as OpenShift secrets and injected as environment variables whereas non secret settings are injected from a yaml file. For this reason, we needed to be able to set each database setting separately.

This Release also includes a number of bug fixes:

• update the demo course to hawthorn.1 to match the version of edxapp that we are running,
• fix platform name and description default values to avoid deserialization bug in Open edX while waiting for a fix on edx-platform,
• set a default configuration for password complexity so that automatic creation of users with "/auto_auth" works by default in development,
• add vim editor to development container.