allow marking WebappVersion as ' not published'
Currently all versions of a webapp are visible to the other users and can be used to run jobs.
This is a burden when when a webapp owner is working on a version which is not yet ready to be published. Such owner would like to commit a version as a 'draft' not visible to the other users.
There is a 'published' flag in the WebappVersion model meant to implement this behaviour, but it is not supported in the UI.