Add X-Requested-With header to all requests

oC 10 uses this header to determine whether a request is an ajax
request. If we want to get rid of this, we need to make sure it's
not used anymore. For example currently it's used to determine
whether a PROPFIND on a password protected link should show
an auth popup or not.

src/helperFunctions.js

@@ -196,6 +196,7 @@ class helpers {
  headers.Authorization = this._authHeader
  }
  headers['X-Request-ID'] = uuidv4()
+ headers['X-Requested-With'] = 'XMLHttpRequest'
  return headers
  }