Split multiple-item modification jobs into chunks

The EWS server is only able to handle around 100 items inside a
request at a time. This applies to all requests that accept multiple
items. To allow mass item updates it is necessary to split large
series into chunks.

This change applies this modification to the mail item update job.

Updates are split into 10-item chunks. While it is well under the
limit, such a small chunk size does not increase overhead too much and
it allows more responsive progress reporting.

The modification also adds progress reporting, now that the
infrastructure is there. This should additionally fix the Akonadi
socket timeout errors that could have been caused by the resource
being busy for long periods of time without any message sent to/from
the resource.

A dedicated helper template class has been added to help reduce
boilerplate when adding chunk splitting into more request types.

Signed-off-by: Krzysztof Nowicki <krissn@op.pl>