added AttributeStatus bit flag

ensure DeviceStatus is a valid bit flag.
[docs] added running tests section to contribution guide.
make sure UI correctly treats scrutiny failures as failed.

webapp/backend/pkg/models/measurements/smart_attribute.go

@@ -1,7 +1,9 @@
 package measurements
 
+import "github.com/analogj/scrutiny/webapp/backend/pkg"
+
 type SmartAttribute interface {
 	Flatten() (fields map[string]interface{})
 	Inflate(key string, val interface{})
-	GetStatus() int64
+	GetStatus() pkg.AttributeStatus
 }