force Sqlalchemy-Utils<0.24

Conflicts:
	etc/deps.txt
Added sqlalchemy type: UUID

Conflicts:
	abilian/core/sqlalchemy.py
deps: oddly lxml was not listed
use pathlib, added data_dir in instance folder

Conflicts:
	abilian/app.py
	abilian/testing/__init__.py
	etc/deps.txt
added repository service: store binary content by uuid key

Conflicts:
	abilian/app.py
	abilian/services/__init__.py