Adds the inspector commands to lispkit

Keybinds:

- `C-x-i-o`: opens inspector
- `C-x-i-c`: closes inspector
- `C-x-i-a`: attaches inspector
- `C-x-i-d`: detaches inspector

`C-x-i` was chosen because "inspector".
@joachifm no, the inspector is there. I can't open it as long as the option is set to nil though.