Add EditorAlias to content value outputs

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

Description

The pending clipboard feature (and in part also block level variance) would benefit greatly from knowing up-front what kind of value editor is backing a content property value. To achieve this, we need an "editorAlias" property to each value in the content endpoint outputs (documents, media, member).

There will be a follow-up to this at block level for block level variance.

Testing this PR

1. It should be possible to edit and save existing documents, media and members. Make sure you test this on items with properties 😄
2. Also verify that collection views still work as per usual (try a media folder).
3. Lastly, the output from a content endpoint (i.e. GET document) should contain editorAlias for each property value:
   

[nikolajlauridsen]

Looks good, tests good 👍