Outline improvements

Functionality of the outline view could be improved.

• when navigating in the ttcn3 source code, the corresponding outline element should be selected
• autoselected outline item should be expanded if it is currently collapsed
• it is almost impossible to find an inactive selected item when using dark theme
• indicate deprecated elements with strikethrough (depending on semantic highlighting setting)
• add type info for outline elements
• try implementing hover support providing doc comment and code peek (due to Eclipse limitation)
• add outline preferences page
• notify outline to refresh after incremental updates
• add support for the non-standard @category tag
• implement filtering based on @category
• add toggle button for imports