Add Qt prompt for unlocking wallet, always enable privileged menu
buttons

The privileged menu buttons are now enabled all the time, and if the
user clicks them when the wallet is locked, the user is prompted to
unlock the wallet.
Issue #3: Initial work on processing custom URLs into something useful

So far, custom URLs have been completely ignored. Now they're parsed (on
OSX) and then completely ignored.
Don't exit dirty in release mode

Force a clean exit in release mode. I don't care. Just do it.