WIP: add 2 extension loadouts, one "Usability" loadout, one "Strict" loadout

This MR will ultimately enable the use of 2 profile types for Firefox and Chrome, known as "Usability" and "Strict" modes. Currently, it only adds the ability to build a "Usability Mode" installer, using the ./experimental.sh buildscript on Windows in git bash will result in a Usability-mode installer(assuming all build-dependencies are satisfied). When it's ready, it should just be one installer, with the ability to select a profile at install-time.

See also:

• http://zzz.i2p/topics/3367-strict-and-usability-modes-against-browser-fingerprinting
• http://i2pgit.org/i2p-hackers/i2p.firefox/-/issues/8
• http://i2pgit.org/i2p-hackers/i2p.firefox/-/issues/4
• http://i2pgit.org/i2p-hackers/i2p.firefox/-/issues/3
• http://i2pgit.org/i2p-hackers/i2p.firefox/-/issues/1