Push of some queued changes to EWS resource

[Krzysztof Nowicki]

Hi Laurent,

I haven't had a chance to work much on the EWS resource in the last couple of years unfortunately. This doesn't mean that I haven't done any work. During that time I've done some improvements and bug fixes, which I have been testing during my daily work.

I think the time has come to push them, especially that I saw 21.08 has being branched recently and trunk opened for general development towards 21.12.

My backlog of changes consists of 38 commits - mostly some minor improvements and bug fixing, notably including:
 * Chunked requests for most operations on multiple items. Internally Exchange doesn't allow a single request to operate on more than 100 items. This would have caused failure when trying to for ex. delete hundreds of e-mails in one operation. With this change the operation is split into several requests.
 * Rework of background, server-triggered updates (subscriptions). These are now done in background and don't block the resource's state machine towards the Akonadi server.
 * Migration of collection sync state from the configuration file to per-collection attributes.
 * Reduced number of forced collection synchronizations due to conflicts with locally modified items.
 * Implementation of progress values for many operations, including the long-lasting full collections sync job.
 * Fixes to device key OAuth authentication, which broke due to Microsoft server-side changes.

Please let me know if it's fine for me to push them, or if you'd rather like them reviewed first.

Regards
Chris