it seems that prefixiter is expected to return child *folder* but was relying on a specific .children implementation, fix this

3.6 api update, cleanup

[forms] let the autoform specify the generic relation field label, no need for a custom fieldset, may be handled as for other fields by the renderer.

simplify messages used for inlined forms

should have been in previous commit (moved below in the module)

[forms] the last touch: handle inlined relation forms as fields by introducing a simple InlinedRelationField. This makese things more flexible while removing a lost of overriding necessary.

fix label handling: when label is explicitly set to None, don't try to guess it

surrounding div necessary for proper error localization

cleanup base class

by default use new jquery widgets for Time/Date/DateTime fields

new jquery based widgets for Time/Date/DateTime, backported from crm

introduce a default render implementation on the base widget, which add_media and then call the newly introduced method _render(form, field, formrenderer), abstract of the base widget class. This allow a litle code factorisation and avoid to forget the call to add_media in subclasses.