#open_children_from_content: added a button at the bottom of fragment content
#refactoring: extracted piggydb.widget.FragmentNodeToggle
Merge branch 'master' of github.com:marubinotto/Piggydb
#open_children_from_content: added logic to show the button only when the node toggle is collapsed
#open_children_from_content: changed the button markup
#open_children_from_content: added logic to control the visibility of the button
#open_children_from_content: added logic to the button to work