Introduce "Verified" badge in SecureDrop directory

[eloquence]

Once we have completed epic #488, we can get serious about the ultimate goal of this project: making the SecureDrop directory more inclusive of most known instances (except those with egregious security issues) and simplifying addition/removal. This will necessitate the following steps, which will be broken into separate issues as we get closer to working on it:

• Add support for "Verified" badge (see [scanner integration] Finalize icon set for directory badges #489 for icon) to SecureDrop directory
• Finalize verification standards (proposal)
• Split Instance Verification Form into separate forms, e.g., "Submit Instance" vs. "Get Verified"
• Add "Verified" badge to currently listed instances which already qualify
• Notify all news organizations currently in the directory about (re-)verification process. We'll have to notify all to ensure they understand how the new process works, e.g., we may need to re-verify details with them intermittently.
• Add all missing instances (Nagios is fairly complete) to the SecureDrop directory. Reach out to points of contact where we have them, to ensure logo/description/categories are accurate and inform them about verification process.
• Draft and publish a SecureDrop.org blog post about all of the above

Out of scope:

• Self-administration of directory data
• Adding email contacts to SecureDrop.org