Feature/rails3 fix planning element api

* when reading and writing planning_elements fields were named inconsistently
* the name attribute in planning_element_journals was rendered as a namespace, instead as a name attribute
* times should be in iso8601, but they weren't
  `Time.now.utc #=> 2013-10-07 14:39:32 UTC` <-- **THIS IS NOT ISO8601** <sup>(2013-10-07 14:39:32Z is right)</sup>

  ![](http://imgs.xkcd.com/comics/iso_8601.png)

* do not listen for `planning_element_type_id` anymore, it is now named `type_id`

see https://www.openproject.org/issues/2297