Address ActivityDetail view TODOs

[BeltranDaniel]

Summary.
In the app activities the ActivityDetail view is missing the implementation of the post method, as shown by the TODOs in the next fragment of code.

WebSiteAPI/acm_web_site/apps/business/activities/views.py

Lines 56 to 60 in 8e84102

	def post(self, request, pk):
	member_serializer = MemberSerializer(data=request.data)
	print(member_serializer)
	# TODO: Handle all info received from its form instead of printing
	# TODO: Take into account all many-to-many relationships in the serializer