Add exit code map to release config to allow displaying different messages for other status codes

[nefarius]

Some setups do not just have one "success" condition, for example if the user decides to skip a mandatory reboot, msiexec exits with a different exit code. Add a map to the remote JSON that allows the distributor to specify something like <code>: "Alternate success message for UI" so the user can be informed that the update succeeded, however the new version might only work properly after the reboot has been issued. Maybe there is also some simple way to allow a bit more UI customizing like adding a help button that opens a URL.