Release v0.2.0

Production release of the DruLab browser extension.

Fixes since v0.1.6:
- Manifest version is now injected from the release tag, so the installed
  extension reports the correct version (#95).
- Firefox gecko.update_url is gated behind the signed release, so unsigned
  install-from-file no longer reports 'corrupt'; the signed .xpi keeps
  update_url for auto-update (#95).
- Reset Storage works in Chrome's embedded options dialog (replaced the
  CSP-suppressed window.confirm with an in-component two-click confirm) (#95).
- Debug helper page no longer uses inline script/onclick/innerHTML, clearing
  the Firefox CSP INLINE_SCRIPT warning (#96).
- Plus the features accumulated since 0.1.6 (parallel pollers, last-update-type
  indicator, keyboard scroll-focus, Android APK release flow, and more).