Better automation of building process (auto-deploy staging)

[TRtomasz]

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Description Currently staging environment is almost not used. We should change the building process more automated. It would improve testing a lot.

1. Add new branch called master. New process would be like this:
2. New functionality is being developed. Checked by developer locally.
3. Merge request, code check, approved and merged to the development branch
4. Automatic build(from development branch on staging.stremio.com) is triggered after merge or There is only one automatic build once per day but we also make it possible for developer to trigger it manually. We could have 2nd shell app that will be using staging for users to test new features.
5. Build has test pipline/stage added.
6. Build is successful. Now it can be tested manually.
7. New functionality/issue solution is approved by a tester. We decide that new release is ready, then:
8. Run cut release(with proper flags like "ShellOnly" "WebUIOnly" "ALL") - it will merge development branch to the master, deploy new version production environment. Create tags, update docker files, update download links could even create new posts on social media.