Fix for #1706: ceylondoc does not list enumerated cases

Added an enumerated icon decorator and make it clear which tab to use to find enumerated types
Fix for #1715: ceylondoc: move documentation to a tab
Tests for #1706: ceylondoc does not list enumerated cases
Fix for #1716: ceylondoc: move inner types below initialiser/attribute/method
Fix for #1706: ceylondoc does not list enumerated cases

New icons