Fixes mozilla#58

Pick commits
- 20daa86: Revise git hooks (#68)
- 81d0024: Revise `destroy_cubeb_device_info` (#67)
- 1cc8a31:  Add a hook to check that commits are formatted and linted correctly (#66)
- aa80b3f: Try using the model id as group id. (#64)
- ab31978: Bail if `cargo clippy` or `cargo fmt` fails (#65)
- 3860bb3: Fix comments in #57 (#63)
- ef5f58b: Run `cargo fmt` and make scripts executable (#62)
- a4c83db: Fix two bugs and add logs (#57)

Differential Revision: https://phabricator.services.mozilla.com/D68402

--HG--
extra : moz-landing-system : lando

…"about:config" to stop forcing opaque backgrounds. r=tabbrowser-reviewers,dao

The background behind the rendered webpage may now be made transparent with these changes by toggling the mentioned preference.
The new option defaults to false, preserving the previous behaviour as the default. For the changes to apply "browser.tabs.allow_transparent_browser" has to be explicitly set to "true" in about:config.

For transparency to actually work, though, a userChrome.css is necessary to make the tab's background transparent ( :root { --tabpanel-background-color: #63 !important; } ).
Pages may not be transparent by default (except for some rare cases), but extensions may be used to enforce transparent background colors on all pages.

As such this patch implements all necessary changes to allow users to make firefox transparent without having to patch and recompile it.

Differential Revision: https://phabricator.services.mozilla.com/D201346