[Mozilla Branding Removal] First pass at removing Mozilla references, links, images, etc.

[Exairnous]

Mozilla links and references have been either removed, updated, or replaced with placeholders. Placeholders are marked with (TBD) where possible.

The PROMOTION.md file has been rewritten to be generic and no longer conveys the automatic right to use promoted scenes in advertising.

The two images with Mozilla branding have been replaced with non-Mozilla counterparts.

More details can be found in the commit messages.

Additional Notes: src/editor/nodes/TroikaTextNode.js should be checked to make sure it isn't a credit and should actually be removed.

links in .env files and habitat files are unchanged to ensure nothing breaks. The same for references to mozillareality

links in yarn-error.log are unchanged because I think they have a historical context. It's possible this whole file should be removed in the future, though.

The reference to Mozilla in src/ui/assets/sources/SketchfabSource.js I have deemed a credit and left unchanged. For reference, this what I left unchanged: label: "Mozilla Playground - by Tombolaso"

I have left these references unchanged as I believe they don't constitute branding:

test/fixtures/V3TestScene.spoke:                  "href": "https://hubs.mozilla.com/scenes/VfoICgK/too-late"
test/fixtures/V4TestScene.spoke                   "href": "https://hubs.mozilla.com"
test/fixtures/V6TestScene.spoke:                  "href": "https://hubs.mozilla.com"
test/fixtures/V7TestScene.spoke:                  "href": "https://hubs.mozilla.com"
test/fixtures/V8TestScene.spoke:                  "href": "https://hubs.mozilla.com"
test/integration/Editor.test.js:                  author: "mozillareality",
test/integration/snapshots/Editor.test.js.md:     author: 'mozillareality',
test/integration/snapshots/Editor.test.js.md:     href: 'https://hubs.mozilla.com/scenes/VfoICgK/too-late',
test/integration/snapshots/Editor.test.js.md:     href: 'https://hubs.mozilla.com',
test/integration/snapshots/Editor.test.js.md:     href: 'https://hubs.mozilla.com',
test/integration/snapshots/Editor.test.js.md:     href: 'https://hubs.mozilla.com',
test/integration/snapshots/Editor.test.js.md:     href: 'https://hubs.mozilla.com',
test/integration/snapshots/Editor.test.js.md:     href: 'https://hubs.mozilla.com',