Add keyboard shortcuts (#92)
This adds six keyboard shortcuts and their entries in the shortcuts dialog:
- Add (Ctrl+N)
- Search (Ctrl+F)
- Select (Ctrl+S)
- Shortcuts (Ctrl+?)
- Preferences (Ctrl+,)
- Quit (Ctrl+Q)
I've used Ctrl+N for Add so it won't be confused with "select all" in other applications.