When playground is created or modified it emits an event. (#225)

The scheduler listens to playground events and updates it's
configuration immediately.

pwd/playground.go

@@ -3,6 +3,7 @@ package pwd
 import (
 	"log"
 
+	"github.com/play-with-docker/play-with-docker/event"
 	"github.com/play-with-docker/play-with-docker/pwd/types"
 	"github.com/satori/go.uuid"
 )
@@ -14,6 +15,7 @@ func (p *pwd) PlaygroundNew(playground types.Playground) (*types.Playground, err
 		return nil, err
 	}
 
+	p.event.Emit(event.PLAYGROUND_NEW, playground.Id)
 	return &playground, nil
 }