Add beta releases to the upgrade notification system
Beta releases will be included in the Spark auto-update process.
Users must opt-in through a Spark setting in the preferences window
The setting is a checkbox in the "Notifications" pane in the preferences window that reads "Check for Beta Updates"
The default is unchecked
When enabled, Spark checks for both beta releases and normal releases
If a new release is available the user is prompted to upgrade, just like it currently works with general releases of Spark
As discussed, a good way to implement this is to pass in an extra param for the web service call to indicate that the a beta release can be returned as the newest.