Reinstate tempstorage

[dataflake]

The latest tempstorage release (5.2) has a fix for the data loss issue that led to a whole series of changes in Zope and its documentation to discourage its use. This is no longer necessary. With a fixed tempstorage the old sessioning configuration that uses Products.TemporaryFolder and Products.Sessions becomes a very attractive option for small deployments again. It works out of the box and requires no separate server process. I will go through the old tasks/PRs and revert them.

For reference, the following tasks/PRs removed or discouraged this use:

• Deprecate / Remove usage of tempstorage #679
• Remove recommendation of tempstorage. #684
• Completely drop support for tempstorage #686
• Remove further tempstorage dependencies. #689
• Document my findings on server side sessions in Zope 4+. #827