Use Crowdin for localization

[oxygen-dioxide]

There are many contributors who want to contribute to OpenUtau's localization. Crowdin provides a user-friendly UI for them to contribute strings translations without having to learn git and code.
I created a crowdin project for OpenUtau at https://crowdin.com/project/oxygen-dioxideopenutau
Changes made to this repo:

• added crowdin config file crowdin.yml and a github action .github/workflows/crowdin.yml to sync this repo with crowdin project
• files outputed from crowdin doesn't follow the code styles used in this repo, so I changed Misc/sync_strings.py to use it to fix their styles
• Crowdin doesn't handle fontfamily, so I store them at unhandled_strings.json, which is applied when running sync_strings.py.

[stakira]

This is great! Could you clarify:

• How to add a new string key, e.g., during new feature development
• How to delete a string key from all languages
• How to add translations. I suppose there is no point to edit axamls, since Crowdin will overwrite them, right?
• How are the translations reviewed? What if someone made a change by mistake?
• How does this affect release cycles. Just run the workflow before making a release?

We would also need some guide in the Wiki later.

[oxygen-dioxide]

Crowdin actions runs in my forked repo at 12:00 UTC+8 every day.

• When running the crowdin github action, English Strings.axaml will be synced from github to crowdin, including new strings and deleted strings.
• Yes, crowdin actions will overwrite existing axamls, so we'll need to edit them on crowdin website. However, if a contributor edited an axaml file, crowdin also provides an "import file" function.
• The translated strings won't directly go into the master branch. Instead, they're synced into https://github.com/oxygen-dioxide/OpenUtau/tree/crowdin-translated when the action runs. Only this branch will be modified by crowdin. We can review what has been changed there. Each time when we are going to release a new version, just create a PR from that branch to official master branch.

[stakira]

Let's try make the process as smooth as possible, i.e., as little human action as possible.
I assume the current flow is:

1. Add text to main repo
2. Merge the new text into to your repo
3. Workflow picks it up and updates crowdin-translated branch in your repo
4. Create and merge a PR from crowdin-translated branch

1, 3 and 4 are fine. But 2 is a manual step. Could we make it pick up untranslated text from the main repo? Or we should run the workflow from main repo instead?

[oxygen-dioxide]

Added these code into crowdin action (before syncs EN strings into crowdin), Now it fetches the latest changes from official repo autometically:

      - name: Sync from official repo
        run: |
          git pull --unshallow
          git remote add official https://github.com/stakira/OpenUtau
          git fetch official
          git merge --no-edit official/master