Replace generic context-menu items with reader-specific, context-aware actions in Paperback

[amirsol81]

When we press the Applications key on a book in Paperback, the context menu shows items like “Select all” and “Copy,” along with “Cut” and “Paste.” The latter don’t work and aren’t really appropriate for a reading app. Instead, it would be more useful if the context menu offered actions that fit reading workflows. For example: “Create bookmark,” “Find,” “Go to page,” and—when some text is selected—options similar to Bookworm such as “Find in Wikipedia” and “Define in Wiktionary.” In short, please replace the generic items with relevant, context-aware commands that also change based on whether text is selected.