CX2: Tool to add new links to the current section (first part)
- When text is selected, show a card corresponding to that selection with options to add a link. The link created this way does not behave like other links - that is in another commmit.
- Introduces a new link tool to add arbitrary internal or external link. Internal links can be searched. On selection nothing happens - that is in another commit.
- Enhanced the tool spec to define event handlers for tools in UI models.