New features

Alpha2 adds the concept of periodic availability - bookable content types may now be specified as "periodically available", meaning that they will default to unavailable and be available only when explicitly made so. This is generally useful for use cases such as offering tours or lessons at fixed time slots.

Fixes of #2962017: Do not force `cron` key to be defined

Initial module release.

- Fixed missing box-sizing on page-info div
- Added readme.md
- Fixed white screen of death bug on Drupal 8.5.1
- Introduced themes for adminic toolbar
- Added first version of configurator for adding links
- Introduced compact mode

Expose Display suite fields as EntityDisplay plugins!

* 6752e1f + EntityDisplay_DsField and configurators.
* 5a20fc7 Remove unused import.
* 26879bc EntityDisplay_FieldWithFormatter: Behavior if $helper is NULL.
* 6d96f67 EntityDisplay_FieldWithFormatter: Remove unnecessary @throws tag.

* 4fa404d Let EntitiesListFormat_SimpleTable use StaticHub functionality, and make it context-aware.
* 9316ed8 + EntityDisplay_SequenceWithListFormat.
* 8ebd6f5 Improve sanity check in EntityDisplay_Sequence::__construct().
* 80c450c Make EntityDisplay_Sequence::$displayHandlers private.
* d5d71bb Let EntityDisplay_Sequence use StaticHubBase functionality.
* eef6f7d + StaticHubBase sub-classes for EntityDisplay and ListFormat.
* 9ea553d + StaticHubBase.
* 19b4fd1 + Configurator_Passthru.
* 5ac42e9 + EntityToEntities_EntityReferenceField.