Updated dependencies, readded Travis CI and added cross browser testing.

Updated all the dependencies to the latest versions supported by Ionic 3.
Readded Travis CI. (Removed in https://github.com/lathonez/clicker/commit/09b1fee37b1c33510a46f4ffe3d3cb503171d6f8.) See the logs here.
- Builds the Android, iOS and Windows (UWP) apps. Should be very easy to deploy them to finish #43.
- Builds the Progressive web app (PWA).
- Runs the Unit and E2E tests in Chrome and Firefox Quantum.
Updated CircleCI and AppVeyor for consistency with Travis CI.
- Updated CircleCI to deploy the production version, which is much faster (Ahead-of-Time (AOT) compiler).
Updated the README.
- Updated instructions to correspond to the updated dependencies.
- Added instructions for testing in Firefox Quantum.
- Minor copy edits.
Fixed production build issue. (Not sure if I fix it correctly, but npm run build -- --prod now runs without an error.)

lathonez / clicker