#31 API protected visibility

* reworks most internal API methods for de/serializing from public to protected visibility
* moves test_api_sharing.py into /share subfolder of tests

api/tests/v1/share/__init__.py

@@ -0,0 +1,7 @@
+"""
+Author: Michel Peltriaux
+Organization: Struktur- und Genehmigungsdirektion Nord, Rhineland-Palatinate, Germany
+Contact: michel.peltriaux@sgdnord.rlp.de
+Created on: 28.01.22
+
+"""