make it possible to pass array to select_options for _edit.field_type_item partial
Refactor how content controller renders fields

Node can specify custom (additional) fields to display by overriding #own_fields_to_display

To override which fields are visible for content you need to override
contontents class .releaf_field_to_display method
Add test to check that Node includes (prepends actually) Releaf::ContentNode module
prepend Releaf::ContentNode instrad of include

This allows Node to override methods of Releaf::ContentNode and call
super

http://stackoverflow.com/questions/4470108/when-monkey-patching-a-method-can-you-call-the-overridden-method-from-the-new-i/4471202#4471202
Update ActsAsNode modules

* remove unsused #node_editable_fields method
* add .releaf_fields_to_display to active record nodes
Add style to hr element in content view