Design a dev icon for Tor Browser

See tpo/applications/tor-browser#43543 for context. The new icon should be distinct from the current Nightly icon.

The devs are suggesting we produce a grayscale version with a different icon in place of the alpha or moon symbol – potentially a cog or other tool of some sort?

We will need the following in the short-term:

• Flat/glyph version
• Adaptive icons for Android

And lower priority, in the longer term (i.e. not needed now, but potentially in the future):

• Windows application icon(s)
• MacOS application icon(s)
• Linux application icon(s)
• Phosphor icon