Service Bus: Scalability improvements

Description

Partitioning and express queues should be enabled by default when creating new topics, to improve performance in the event system in Azure.
When upgrading, no changes are made to existing topics. If you want to enable the new features in Service Bus, delete a topic and let it be re-created.

Compatibility: It is possible to disable both these features in the configuration file:

<episerver.framework>
    <event defaultProvider="azureevents">
      <providers>
        <add name="azureevents" type="EPiServer.Azure.Events.AzureEventProvider,EPiServer.Azure"
              connectionStringName="EPiServerAzureEvents" topic="PartionedEvents"
             enablePartitioning="false" enableExpressQueues="false"/>
      </providers>
    </event>