Increase timeout for reading data from resources to 30 seconds

The introduction of LZMA compression for payloads can mean that when handling already-compressed attachments, especially those in large sizes, the default timeout of 10 seconds can be exceeded. This is particularly evident for machines with rotational disks or full disk encryption.

This has particularly bad effects on item syncing:

1. The resource retrieves an item, and starts compressing the payload.
2. The compression takes more than 10 seconds, so the resource is disconnected from Akonadi due to the timeout.
3. Upon reconnection, there is an attempt to rollback the change, but the change did not actually take place, so a bunch of errors regarding transactions are logged.
4. The database for that resource and that collection is left in an inconsistent state.
5. This can cause the resource to ultimately get stuck on its jobs.

Fixing the actual problem is probably far more convoluted, but a quick workaround would be to increase the timeout up to 30 seconds, to stay on the safe side.

This change was tested on a laptop with FDE that could not sync attachments larger than 5M: after the change, the syncing was performed sucessfully.