Change: Configurable extension autosave

We have added a global setting in the configuration to enable autosave (and the corresponding timeout) for bundled and external extensions,
instead of having a per-extension configuration which was limited to external extensions.
Handling of the provided autosave needs to be taken care of by the extension itself.

https://github.com/owncloud/web/pull/8455
https://github.com/owncloud/web/pull/8457
https://github.com/owncloud/web/pull/8474
