Python Entrouvert

middleware: PythonSettingsMiddleware overload FileBasedTenantSettingBaseMiddleware and not JSONSettingsMiddleware

Closes #5972

New TenantMiddleware which try to find tenants based on the filesystem

If path <settings.TENANT_BASE>/<hostname>/schema exists, read this file an build
tenant modle with Tenant(domain_url=<hostname>, schema_name=file(<path>).read()).

refs #5106

Add middleware to load settings from a JSON file based on the tenant

• Loaded settings are cached based on the mtime of the setting file
• JSON file path is <settings.TENANT_BASE>/<schema_name>/settings.json

refs #5106

multitenenant extension