URLService
Merge branch 'master' into url-service
Move PostgreSQL service to URLService, add missing name and index_name
Convert email service
Convert memcached to URLService

The API is very inconsistent, but preserved for the sake of people using
'hosts' in their configuration
Proxy and Redis services
Redis
Skip tests when a relevant Docker image is not found
API test class generation for services

- A test module generating tests common for all services
- Unify container providers between services
Merge branch 'master' into url-service

Conflicts:
	forklift/services/email.py
	forklift/services/syslog.py
Lens -> Descriptor
Cleanup services in availability test
Fix Elasticsearch availability check
Fix PostgreSQL URLs
Fix Redis availability check
Properly clean up Docker client
Empty lines to separate blocks
Better replace_part API
Merge branch 'master' into url-service

Conflicts:
	forklift/services/base.py
	forklift/services/postgres.py
	forklift/services/redis.py
Formatting