Improve and extend keyboard shortcuts

[Tonemon]

For now we only have the following keyboard shortcuts:

• Ctrl+R: refresh data on current page (overrides browser refresh)
• Ctrl+Space: navigate to home and focus the search box
• Ctrl+K: navigate to knowledge bases
• Ctrl+B: navigate to bookmarks
• ?: toggle keyboard shortcuts help modal (when not typing)

We could add / to focus search, j/k to navigate results, b to bookmark the focused result, o to open the source document.