Update the mdm table link for master only

[mmattel]

References: owncloud/ios-app#1094 ([docs/folder-structure] Changed Docs Structure / MDM)

• This PR sets the mdm_tables link, for master only.
• The table is now dynamically included from the ios-app product repo!
• When having a new branch, we must set the ios-branch attribute in the new branch accordingly.

Note that this PR must not be merged before the referenced ios-app PR gets merged.

Note before merging, we must:

• remove the active attribute ios-mdm-tables-url line (pointing to a path that will get removed)
• activate the remarked ios-mdm-tables-url line
  (pointing to a path that will get added by the PR linked)

A build runs fine locally.

No backport

[michaelstingl]

@mmattel what's needed to move this forward? Anything I can help? (blocks #93)

[mmattel]

Superceded #93