Add a stateful deployment mechanism

[lowell80]

This needs more thought and planning. Likely requiring a long-living feature branch...

This would NOT be used to replace existing Splunk deployment mechanisms (in general), the intended use would be for intelligently writing content from a temporary staging area into the deployment-app, shcluster/apps or master-apps folders.

In some special cases it could be used to deliver to the apps folder, but that should be reserved for situations that Splunk can't handle natively. (For example, there's no way to deploy to the apps folder on an index cluster peer.)