celery: change ini template to use sqlite for results

'amqp://' might be good - also for results, but seems to need additional
non-trivial setup. And according to
https://docs.celeryproject.org/en/3.0/whatsnew-4.0.html#features-removed-for-lack-of-funding
it is deprecated.

Kallithea only uses Celery results when repos are created or forked and user
browsers are reloading pages to poll for completion. amqp seems like
unnecessary complexity for that use case.

Sqlite does however seem like a minimal but fine solution for the Kallithea use
case in most setups.

development.ini

@@ -255,7 +255,7 b' use_celery = false'
 ## Example: connect to the virtual host 'rabbitmqhost' on localhost as rabbitmq:
 broker.url = amqp://rabbitmq:qewqew@localhost:5672/rabbitmqhost
 
-celery.result.backend = amqp://
+celery.result.backend = db+sqlite:///celery-results.db
 
 #celery.send.task.error.emails = true
 #celery.amqp.task.result.expires = 18000

kallithea/lib/paster_commands/template.ini.mako

@@ -361,7 +361,7 b' use_celery = false'
 <%text>## Example: connect to the virtual host 'rabbitmqhost' on localhost as rabbitmq:</%text>
 broker.url = amqp://rabbitmq:qewqew@localhost:5672/rabbitmqhost
 
-celery.result.backend = amqp://
+celery.result.backend = db+sqlite:///celery-results.db
 
 #celery.send.task.error.emails = true
 #celery.amqp.task.result.expires = 18000