IDEMainWindow: Set member as protected
EditorsController: class creation
RecursiveSplitter: Fix useless recursion removal
EditorsController: Implement event filter
Splitter: Set widget uncollapsible by default
MyIdeMainWindow: Use editors controller
RecursiveSplitter: Remove old event filter
StyleSheet: Set style sheet for toolbar in the main window (centralize)
ClosableWidget: Add a place holder
IDEMainWindow: Add toolbar/action to control panel visibility
SidePanel: Make it a Splitter
SidePanelController: Class creation
MyIdeMainWindow: Use SidePanelController
EditorsController: Handle element creation in virtual function

In case we want to make it a mother class
BottomPanel: Make it a ClosableWidget
Create some dummy place holder for test purpose
SidePanelController: Use close button to unsplit
Controllers: Fix split (new element come after)
SidePanelController: Use dummy content for testing purpose