Serverside parsing conversion between AEM and prosemirror formats

[bosschaert]

@karlpauls and I have some changes implemented to move the conversion between the AEM and Prosemirror formats to the serverside. This prevents the document from bouncing a few times between client and server on initial setup and if an updated document content comes in from the server. It simplifies the implementation as there is no risk of multiple clients applying the same change multiple times if there are more clients with the document open. The updated implementation is inside da-collab for now. Karl and I worked last week to integrate it and we have the following 2 PR’s which should make da-collab a lot more stable:

• Parsing da-collab#38
• aem2doc parsing now done in da-collab #127

These would need to be merged effectively together, applying the da-collab change first and then the da-live one.
That said, there is some risk around this because obviously, we're not 100% sure if we don’t run into content that will be problematic while parsing and we might end-up writing back broken stuff to da-admin. Hence, the idea we have is to first merge the following PR:

• Store version content automatically once in preparation for parsing change da-admin#39

The idea with the da-admin PR is that (for now) we will create a real version on an incoming PUT if the last change has been > 1h ago - while the very first time, we’ll create always a version. Hence, if we have that rolled out first, we can at least fix broken content (should it happen). We can work on making this configurable in the future but for now I think it makes a lot of sense to have this.

Finally, if we have these 3 merged, it would be good @auniverseaway if you can get the UI tweaks you had in mind for #110 done, as with that we’ll even have the possibility for other people to recover a version if da-collab broke it.

Thoughts?