add app-template for 26

[kesselb]

#1218 went stale due to many changes ...

Let's tackle it in smaller steps ;)

• Added a dedicated app-template for 26 instead of the symlink to 25
• Application class is now using IBootstrap
• nextcloud/ocp for the matching nextcloud version is installed
• Code style applied

[kesselb]

@bigcat88 I still don't have a working dev setup, would you mind generating another app with this branch and sharing the result?

[bigcat88]

app.tar.gz

[kesselb]

app.tar.gz

Thank you very much 👍

• The generated version for nextcloud/ocp seems right
• composer install works
• composer run cs:fix works and does not find any error (depending on the app name it may find some, but that's unavoidable)
• npm install works
• npm run dev works

This looks okayish to me. At least it's a bit better than before ;)