Make sure Torbutton and Tor Launcher are not treated as legacy extensions

We should avoid that Tor Launcher and Torbutton get treated as second class add-ons due to them still being based on XPCOM (e.g. getting shown on a separate add-on panel and not listed on the default about:addons page).

Setting extensions.legacy.enabled to true and adding the extensions IDs to extensions.legacy.exceptions should fix that.

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information