Fix branch merge when using simple mode

In Nuxeo Studio with BM

• User Solen creates a branch named "newdoctype"
• in branch "newdoctype", Solen creates a doctype called "Toto" extending File
• Solen checks out branch "master"
• Solen merges branch "newdoctype" into "master"
  => branch master shows the "Toto" doctype commits in its history
  => no push button appears

In Nuxeo Platform

• Instance is registered with user Solen
• In admin page, use hot reload
• Create a new document type in a workspace
  => Document type "Toto" does not appear