Various configuration updates to mirror my VIM setup and code in Scala

- Close window with C-F12
- spawn shell with F2 in current folder
- TAB and S-TAB cycle between buffers
- Scala-specific ensime settings:
  * F7 to typecheck
  * C-] goes to definition (and C-t goes back)
  * C-h returns back in the documentation buffer (after a click)
- Also, font (Droid Sans Mono) and a dark theme