minor refactoring
Add a menu item to cytoscape to display the changelog window
Add a method .openChangelogFrame()
Create the action to perform when the menu item "Changelog" is selected
Create a simple window to display a changelog (the checkbox action is not implented yet)
Create a listener associated with the "close" button of changelog window. There is some thing to do here.
Create the changelog controller which can open and set the changelog text. In the future, the text will be retrieve from the database.