Mapbender Starter 3.0.8.1

• Update mapbender/mapbender to v3.0.8.1
• Update mapbender/owsproxy to v3.1.0
• Update mapbender/fom to v3.2.0
• Update mapbender/digitizer to 1.1.70
• Update symfony/symfony from 2.8.49 to 2.8.51
• Update symfony/security-acl from 2.8.0 to 3.0.2
• Update twig/twig from 1.35.3 to 1.40.1
• Update twig/extensions from 1.5.1 to 1.5.4
• Update doctrine/doctrine-bundle from 1.6.4 to 1.10.2
• Update doctrine/doctrine-fixtures-bundle from 2.3.0 to 2.4.1
• Update doctrine/doctrine-migrations-bundle from 1.3.1 to 1.3.2
• Update doctrine/doctrine-cache-bundle from 1.3.3 to 1.3.5
• Update kriswallsmith/buzz from 0.15.2 to 0.16.1
• Dropped arsgeografica/signing requirement
• Dropped gedmo/doctrine-extensions requirement
• Update misc indirect dependencies
• Fix composer.json meta links (PR#89)