Added new 'example' type in ContributionType.java's enum
UI of 'Add Examples...' done
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
Redesigning 'Add Examples...' button
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
Merge pull request #2795 from joelmoniz/addExamplesManagerRebased

Added examples-package as a new contribution type.