use HTMLParser instead of SGMLParser (cf. 0952bee6).

- wrong default uid was used when migrating a site that never use portal_ids
  to generate security uids
- invalidate transactional cache of security uids

This way validator scripts will be called even for empty listboxs, and this
should also remove ERP5Form/Form.py:validate_all KeyError : 'Field listbox is
not present in request object.' messages from the logs

In the first dialog you still select which action to do on which objects, now
you can only select one action. The second dialog is the actual dialog from the
workflow rendered on the context of one document from documents grouped by
state and portal type. This means that if the workflow uses a custom dialog to
set workflow variables, this dialog will be shown and the variables will be
passed to all documents.
Of course some workflows dialog fields have no meaning in a multi-document
transition, that's why there is a mass_workflow_action=True request parameter
to detect this situation and behave accordingly in such case.

remove owner_title from default selected columns, and add creation & modification dates in more columns

portal_caches tool is expected to allow only Cache Factory instances inside.
Fix tests to use Cache Factory instead of Cache Bag.

different kinds of Cache Plugins.
This API change allows developer to create complex cache structures which
can contain arbitrary set of Cache Plugins and / or Cache Bags (Cache Factory).
Extend Cache Factory so it can return RAM based Cache Plugin instance by its Uid.
Fix tests to reflect changes.

contain Cache Plugins.
Unify in one function cache factory uid generation.

Really use memcached backend for testIngestionWithFlare (it was not setup properly).

Add back wrongly removed volatile conversion caching.
Use new set / get Cache bag API.