Change some defaults to more reasonable values

these shouldn't be too controversial.

the key bindings in the connection list are currently very dangerous when using with production systems, e.g. killing the connected lisp is bound to a mere C-k. the function name ```slime-quit-connection-at-point``` is also misleading, but i didn't touch that (i used to think that it's a disconnect, and restarted production systems until i realized why the users complain about lost web sessions).