Create common package

Moves cryptographer to common. Also adds constants and defines the leghtn of the locator to avoid hardcoding it in almost every file

pisa/api.py

@@ -8,17 +8,12 @@ from pisa.logger import Logger
 from pisa.inspector import Inspector
 from pisa.appointment import Appointment
 from pisa.block_processor import BlockProcessor
+from common.constants import HTTP_OK, HTTP_BAD_REQUEST, HTTP_SERVICE_UNAVAILABLE
 
 
 # ToDo: #5-add-async-to-api
 app = Flask(__name__)
-
-HTTP_OK = 200
-HTTP_BAD_REQUEST = 400
-HTTP_SERVICE_UNAVAILABLE = 503
-
 logger = Logger("API")
-
 watcher = None