Editing the workfow graph

User can edit the graph on the "Graph" tab of a workflow definition feature instance. For editing the graph the user can:

1. drop some nodes among the available list of node templates.
   After a node is dropped, a modal popup is displayed, in which some information have to be filled, some mendatory, some not, this depends on the node template that has been chosen. Forms are displayed in various tabs. A check should prevent the user from closing a popup if not all the mendatory informations have been filled, on all the tabs of the Node configuration popup. (TODO: we need to provide a table with all the fields that are displayed, editable, as well as all the tabs, for all the available built-in templates.)
2. connect the nodes between themselves.
   In the Node configuration popup, there is a transition tab, in which the user should declare all the possible transitions from that node. From those declarations, some "hook points" are displayed around the node, so as to pull the corresponding transitions to other nodes. When saving the graph, a check should inform the user that some transitions have been defined on the graph but are not used (giving names of the missing transitions).
3. User can update a node configuration by clicking on the edit icon that is on the node (same icon as on a widget for editing its properties)

Note: Ideally, we would like to define transitions infromation on the links directly, but it seems like there are some difficulties to achieve this, that's why we propose on this ticket to list the transitions in the parent node before being able to pull them.

Graph creation and edition.

(We must study the possibility to have a "full scren" option for the graph editor)
+ generate xml contribution for the workflow definition