Added feature to allow user to have a wildcard for selecting "Any Pipeli...

...ne" or "Any Stage" within a pipeline when subscribing to email notifications.

This pull request is to let a user select to get notifications for any event on all pipelines or all stages on a particular pipeline.

This is useful because it allows users to be able to be notified on events for a pipeline when it changes without having to update their notifications everytime a pipeline changes.
Damn. Wrote a big comment here and it went away. :(

I had said, the ```hasSubscribedFor``` method goes through every notification filter of the user and matches it against the given pipeline name and stage name. Now, it is called three times. I was wondering what you feel about moving that behavior into ```hasSubscribedFor``` method itself. Instead of three calls, there could be one call here, and the method can change to something like:

```
public boolean hasSubscribedFor(String pipelineName, String stageName) {
    for (NotificationFilter notificationFilter : notificationFilters) {
        if (notificationFilter.appliesTo(pipelineName, stageName))
            return true;
    }
    return false;
}
```

and notificationFilter.appliesTo() can itself take care of the ANY_PIPELINE, ANY_STAGE check. It'd be a method very similar to (and maybe reuse parts of) the ```matchStage``` method. What do you think?