Contributed Examples tree displays in Examples window

Also, example folder does not show as node in JTree
Contribs now show in Example Manager
Modes now taken into account when deciding whether to show examples
Updating display style of Examples Tree
Rename to Examples-Package
Using identifiers instead of names for modes
Redesigning 'Add Examples...' button
Changed Examples Tree structure
Added 'Add Examples...' option to Open Toolbar Menu
Solve old folders displaying
Added function to colourize alternate rows of a JTree

Thus improving the Examples Tree UI appearance