push down app listeners to a datastore (#742)

* push down app listeners to a datastore

fnext.NewDatastore returns a datastore that wraps the appropriate methods for
AppListener in a Datastore implementation. this is more future proof than
needing to wrap every call of GetApp/UpdateApp/etc with the listeners, there
are a few places where this can happen and it seems like the AppListener
behavior is supposed to wrap the datastore, not just the front end methods
surrounding CRUD ops on an app. the hairy case that came up was when fiddling
with the create/update route business.

this changes the FireBeforeApp* ops to be an AppListener implementation itself
rather than having the Server itself expose certain methods to fire off the
app listeners, now they're on the datastore itself, which the server can
return the instance of.

small change to BeforeAppDelete/AfterAppDelete -- we were passing in a half
baked struct with only the name filled in and not filling in the fields
anywhere. this is mostly just misleading, we could fill in the app, but we
weren't and don't really want to, it's more to notify of an app deletion event
so that an extension can behave accordingly instead of letting a user inspect
the app. i know of 3 extensions and the changes required to update are very
small.

cleans up all the front end implementations FireBefore/FireAfter.

this seems potentially less flexible than previous version if we do want to
allow users some way to call the database methods without using the
extensions, but that's exactly the trade off, as far as the AppListener's are
described it seems heavily implied that this should be the case.

mostly a feeler, for the above reasons, but this was kind of odorous so just
went for it. we do need to lock in the extension api stuff.

* hand em an app that's been smokin the reefer

api/server/apps_create.go

@@ -28,23 +28,11 @@ func (s *Server) handleAppCreate(c *gin.Context) {
 		return
 	}
 
-	err = s.FireBeforeAppCreate(ctx, app)
-	if err != nil {
-		handleErrorResponse(c, err)
-		return
-	}
-
 	app, err = s.datastore.InsertApp(ctx, app)
 	if err != nil {
 		handleErrorResponse(c, err)
 		return
 	}
 
-	err = s.FireAfterAppCreate(ctx, app)
-	if err != nil {
-		handleErrorResponse(c, err)
-		return
-	}
-
 	c.JSON(http.StatusOK, appResponse{"App successfully created", app})
 }