Remove runtime dependency on pry and pry-nav.
Start work on GUI implementation using Vedeu.

- Update interfaces, add exit command, use Vedeu::Launcher.
- Add require for Vedeu, change order for requires for GUI.
- Remove dispel, curses and pry-nav;
- Also, update pry to 0.10.0.
- Bump version of vedeu gem to 0.0.32.
- Make interface declarations compatible with vedeu 0.0.32.
- Add mechanism to launch into GUI mode.
- Add space around conditionals to aid readability.