docs: Address quickstart guide issues

[BrianJKoopman]

Description

This fixes several user reported issues in the quickstart guide, the big one being persistent storage of grafana/influxdb data. Other items on my list were:

• Add sudo to user creation steps.
• Add -E to sudo usage when running docker-compose up -d.
• Fix link to Docker installation docs.
• Remove mention of setup.py during installation.
• Point out Agent Reference pages when discussing the site config file.
• Persist influxdb and grafana storage in quickstart example. (Also added to the longer example under "System Configuration".)
• Warn users more clearly when removal of data volumes would cause data loss.
• Update the SCF/dockerfiles with a better recommendation for how to configure wamp_server location with respect to whether we're on the host system or in a docker container. (This is also a big one, and I hope will lead to less confusion about this, as it's perhaps the most common misconfiguration on new systems.)

Motivation and Context

Resolves #238.
Resolves #210.
Resolves #119.

How Has This Been Tested?

I ran through these changes in a clean VM, though I'm maybe not the best test...

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• Unless I am preparing a release, I have opened this PR onto the develop branch.

[BrianJKoopman]

Fixed some small warnings showing up on builds, and resolved some conflicts that arose after the ocs-web removal. Will merge when checks finish.