Stunner - Inline text editor & usability improvements

This tickets follows up on https://issues.jboss.org/browse/JBPM-6777

The goals for this ticket are focused on improving the usability:

• *Show the text input "inline" *within the shape, at the same location where the resulting text that appears once for the shape once set.
  • For example: for a task, the text input should appear at the center of the shape and it should have the right size in order to result as it's being added "inline"
  • This way for a task the txt input will appear at the center, but for an event or for a gateway, it will appear at the bottom

• Add some default place-holder in the text input, if empty (like "Add text here..")

• Show the text input once a new element is being created (either from the toolbox or from the palette) - this will result in both contextual menu and text editor visible, and the text editor also will have the focus. (By pressing [ESC] it can be closed too)

• About closing the text input popup
  • Actually it only it's closed either when clicking on the "X" button it provides or either when double-clicking on another shape, as it opens the text editor popup for this shape
  • When pressing [ESC]
  • I propose closing the popup, if present, once clicking on the canvas as well, WDYT srambach rhn-support-eclayton mstevens1_jira??

See some mocks for this in https://issues.jboss.org/browse/JBPM-6424

Technical details
Here are some technical details about how the name input can be displayed once creating new elements:

• Actually the CanvasInPlaceTextEditorControl adds handlers into the shapes for showing the popup, that's fine
• Once a new element is being created in the canvas an event is being thrown -> CanvasElementAddedEvent - this event contains the element instance, so you can try to just listen (observe) for that event in the CanvasInPlaceTextEditorControl, and then show the popup for it.