Issue #2091397 by vijaycs85, batigolix, targoo, jhodgdon | ifrik: Create hook_help for Datetime module.

Issue #2152217 by joelpittet, mgifford, vijaycs85, jjcarrion, sun: Remove theme_form_required_marker() from the theme system - use CSS instead.

Broke HEAD.

This reverts commit 0f0edea2.

Issue #2095195 by yched, fago, Berdir, amateescu, swentel, pfrenssen, Xano: Remove deprecated field_attach_form_*().

Issue #2177469 by Gábor Hojtsy, Aron Novak, swentel, andypost, Berdir: Move node base widgets to the top level of the form.

Issue #1989468 by plopesc, yched, Wim Leers, effulgentsia: Weird messing with 'default_value_function' in date widgets.

Issue #2080067 by beowulf1416, netsensei: Remove Unused local variable $has_time from /core/modules/datetime/datetime.module.

Issue #2050835 by Berdir | yched: Move Widget, Formatter, and FieldType plugin types to the Core\Field system.

Issue #1953408 by swentel, aspilicious, andypost, yched: Remove ArrayAccess BC layer from field config entities.

Issue #2000384 by yuradoc, Damien Tournoud, alexpott: Fixed php-intl module causes problems with Date and Time fields when editing Basic Page.

Issue #1963476 by widukind, joelpittet, jenlampton, tlattimore, kattekrab, siccababes, adamcowboy: Datetime.module - Convert theme_ functions to Twig.

Issue #2025991 by plach, David Hernández: Introduce hook_entity_prepare() to generalize hook_node_prepare().

Issue #1969728 by yched, effulgentsia, swentel, fago, plach: Implement Field API 'field types' as TypedData Plugins.

Issue #1950632 by effulgentsia, Wim Leers, amateescu, yched: Create a FieldDefinitionInterface, decoupled from  and  config entities, and use it for formatters and widgets.

Issue #501428 by KarenS, swentel, tim.plunkett, webchick, effulgentsia, nod_, scor, Lars Toomre: Added Date and time field type in core.