Lib::IDEWidget: Create IDE Widget library

- Sub-class QSplitter and QSplitterHandle (for visual propose)
- class ClosableWidget
  A widget with a toolbar ending by a close button
  and settable split action
- class ClosableWidgetElement
  A widget to install in a ClosableWidget contain actions for the toolbar
  and a name
IDEMainWindow: Add principal elements
Lib::IdeWidget: Creat class ClosableWidgetEvent

To handle close/split/unsplit event in ClosableWidget
ClosableWidget: Remove ownership member
ClosableWidget: Connect action to ClosableWidgetEvent
Splitter: Gradient modifications
Lib::IdeWidget: Creation of an enum file
Lib::IdeWidget: RecursiveSplitter creation
IDEMainWindow: Splitter ajustement
EditorsArea: Use RecursiveSplitter (test)