Several Wiki documentation view improvements.

* Pin Selection toggle button added to Documentation view toolbar
* Added support for linking to internal documents within the Simantics database in wiki documentation: [[Media:root://Documents/Document.pdf|This is the anchor text for the created link]]
** DocumentDialect will transform links like this into external links that look like this: [http://simantics-internal/http://Projects/Development%20Project/Project/Documents/Document.pdf This is the anchor text for the created link]
** Obviously external browsers and viewers do not understand these links but when these links are clicked in the Workbench Documentation view, the Browser component location changes are intercepted by the function returned by org.simantics.document.ui.function.All.locationChanging and the workbench's default action is performed for the database resource/variable that the URI in the link resolves to in the Simantics database.
* DiagramViewerSelectionProvider.SelectionElement will now return a the variable of the diagram composite when element selection is the diagram resource itself. This helps the Documentation view show the wiki page of the diagram composite when nothing is selected on the diagram editor.
* Fixed a couple of typos from org.simantics.scl.reflection.internal.registry.Namespace
* org.simantics.views.ontology now supports defining SWT RowLayout/RowData for modelled composites. This is used in the Documentation view to flow all the action buttons above the text editor to separate rows even when the view is not wide enough to fit all buttons on a single row.

refs #6449