fix: Remove attributes and meta attributes before persisting docs

Those doc's attributes are specific to the JSON API and should not be
inserted into the Pouch database

This implies that we will have a difference on documents regarding if
they are served through the cozy-stack or through a local PouchDB, the
first one may include those fields in their result, but not the second
one

So from now we should avoid, as much as possible, to relies on the
`attributes` member to prevent bugs on Offline mode. Multiple commits to
fix usages of `attributes` in cozy-client will be done after this one

Usage of `attributes` and `meta` members on cozy-app will also have to
be fixed. This will be a requirement to implement Offline mode on
cozy-apps

This replies to #1486 (comment)

Author: Ldoppea

packages/cozy-pouch-link/src/CozyPouchLink.js

@@ -391,17 +391,44 @@ class PouchLink extends CozyLink {
     }
   }
 
-  async persistData(data, forward = doNothing) {
+  sanitizeJsonApi(data) {
     const docWithoutType = sanitized(data)
-    docWithoutType.cozyLocalOnly = true
+
+    /*
+    We persist in the local Pouch database all the documents that do not
+    exist on the remote Couch database
+
+    Those documents are computed by the cozy-stack then are sent to the
+    client using JSON-API format containing `attributes` and `meta`
+    attributes
+
+    Then the cozy-client would normalize those documents by spreading
+    `attributes` and `meta` content into the document's root
+
+    So we don't need to store `attributes` and `meta` data into the Pouch
+    database as their data already exists in the document's root
+
+    Note that this is also the case for `links` and `relationships`
+    attributes, but we don't remove them for now. They are also part of the
+    JSON-API, but the normalization do not spread them in the document's
+    root, so we have to check their usefulnes first
+    */
+    const sanitizedDoc = omit(docWithoutType, ['attributes', 'meta'])
+
+    return sanitizedDoc
+  }
+
+  async persistCozyData(data, forward = doNothing) {
+    const sanitizedDoc = this.sanitizeJsonApi(data)
+    sanitizedDoc.cozyLocalOnly = true
 
     const oldDoc = await this.getExistingDocument(data._id, data._type)
     if (oldDoc) {
-      docWithoutType._rev = oldDoc._rev
+      sanitizedDoc._rev = oldDoc._rev
     }
 
     const db = this.pouches.getPouch(data._type)
-    await db.put(docWithoutType)
+    await db.put(sanitizedDoc)
   }
 
   /**