Default PR Tasks event handler config doesn't deserialise properly

One of the config options for the built-in event handler that creates default pull request tasks is the numeric ID of the user under whose name the tasks (and their parent comment) will be created. Under the current serialisation scheme this should be an integer (or a singleton list of integers), but certain customers' configs (perhaps ones from an older version of SR?) have it as a string (or list of strings). The strings in question appear always to represent integers anyway, so it should suffice simply to parse them as such at some point in the back end.