… for mssql and mysql

prepared queries pubsub

- Unchanged behaviour without item ids
- Slight changes if item ids are provided:
  - Results are fetched one by one - should be fast enough
    as there shouldn't be too many IDs and there is a way to limit this.
  - Results have the same order as item ids - this is more intuitive
    for the end user, XEP-0060 does not specify this
  - max_items with item ids is a combination not mentioned in the XEP,
    but still supported for completeness.

- Separate INSERT and SELECT to work on all DBs
- SELECT the entire row as this query is already prepared
    and is not much more costly

- Insert parents one by one
- Always delete old parents on update to prevent the corner case
    when all aprents are deleted.

Traverse nodes one by one - it might be slower,
  but complex collection structures shouldn't be used frequently.

Prepared queries for PubSub - part 2