metatag 8.x-1.0-beta1

This is the first release of Metatag for Drupal 8. A huge thank you to Michelle and larowlan for all their help putting this together, and to everyone else who contributed.

There are many other tasks to go before this is ready for a 1.0 release, but this is a reasonable starting point. Stay tuned for more!

• Initial port by DamienMcKenna and Michelle.
• #2563663 by kikoalonsob: Don't convert the title to a string.
• #2563621 by jmolivas: Fixed DrupalConsole integration.
• #2579865 by afi13: Fixed definition of MetatagEmptyFormatter::viewElements().
• #2563667 by vincic: MetatagManager should only be used for objects implementing ContentEntityInterface.
• #2569043 by Michelle: Field defaults weren't loading (core API change).
• #2579295 by Michelle: Fixed the field cardinality limitation.
• #2563667 by Michelle: Follow-up to add missing namespace.
• #2584835 by DamienMcKenna: Fixed double-HTML encoding of the page title.
• #2563637 by larowlan: Added some initial tests for the field type.
• #2596753 by Michelle: Don't encode apostrophes in the page title.
• #2576695 by Andrej Galuf, larowlan, DamienMcKenna: Double slashes in URLs were being replaced.
• #2603548 by DuaelFr: Clear our the head_title array to avoid the site name being added a second time.
• #2617192 by larowlan: Fixed tests due to a core API change.
• #2609138 by rakesh.gectcr: Removed unnecessary 'use' statements.
• #2593149 by larowlan: Inject dependencies into MetatagManager.
• #2593153 by larowlan: Inject dependencies into MetatagToken.
• #2593141 by larowlan: Add a MetatagManagerInterface to avoid type-hinting concrete implementation.
• #2581351 by Michelle, larowlan, DamienMcKenna: Don't save default values to the field, allow them to inherit from the default field settings.
• By DamienMcKenna: Updates to the README.txt file.
• #2572469 by rakesh.gectcr, DamienMcKenna, jaxxed, timmillwood: Added a composer.json file.
• By DamienMcKenna: Added a LICENSE.txt to enforce the license on git mirrors.