fix: serve favicon.ico and robots.txt from WHITENOISE_ROOT

[paulschreiber]

Description

Serve favicon.ico and robots.txt from WHITENOISE_ROOT .

Remove old template view for robots.txt

Partially addresses https://github.com/freedomofpress/fpf-www-projects/issues/581

Changes proposed in this pull request:

Type of change

• Bug fix
• New feature
• Vulnerabilities update
• Config changes
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires an admin update after deploy
• Includes a database migration removing or renaming a field

[harrislapiroff]

Ack, I hate to be so nitpicky about this multiple times, but I think this isn't the right solution either for two reasons:

1. The result of this is that our javascript files in that directory will now also be served at the root (so piwik.js will be available at https://securedrop.org/static/js/piwik.js and https://securedrop.org/js/piwik.js and, while I can't think offhand of any problems that would cause, it's at least weird. (It would cause a problem if someone added a folder name that collided with a page URL, e.g., if someone added static files relating to the directory to /securedrop/static/directory/ that would cause the directory at https://securedrop.org/directory/ to stop working in a way that might confuse a future dev. This is a bit contrived, since that probably isn't where they would add such files.)
2. More importantly I think this directory structure kinda muddies the distinction between the files we want to serve at the root and the ones we want to serve under /static/ which could be potentially confusing to a future developer more distant from this change.

I'd suggest either:

1. Move favicon and robots to /securedrop/static/root/ and make this WHITENOISE_ROOT = os.path.join(BASE_DIR, "securedrop", "static", "root"). The root files will still end up getting served twice, but at least the intention will be clear—and polluting the /static/ namespace is less high-stakes than polluting the root of the site.
2. Create a separate directory at /root_static/ or similar and put the files in there and change this to WHITENOISE_ROOT = os.path.join(BASE_DIR, "root_static"). I prefer this solution for minimal ambiguity, but I'm not wedded to it.