Make sure dcrd and dcrwallet shutdown when app closes.
Make sure dcrd and dcrwallet shutdown when app closes.

Prior to this, on Linux dcrd and dcrwallet stayed open after closing
decrediton.
On macOS they were closed automatically but not given a chance to shut
down cleanly.

This tells them to shut down cleanly on both.

Only done in production mode.

Closes #135

decred/decrediton,decred/decrediton,oktapodia/decrediton-appveyor-test,decred/decrediton,oktapodia/decrediton-appveyor-test,decred/decrediton,decred/decrediton,oktapodia/decrediton-appveyor-test,decred/decrediton,oktapodia/decrediton-appveyor-test,oktapodia/decrediton-appveyor-test