added missing require attribute_select
Merge pull request #24 from cboelter/fix/missing-select-attribute

added missing require attribute_select
fix to few arguments in usedonly query
readded value_id as value and updated the queries
sql code style
Add php 5.6 to .travis.yml.
Switch to ccabs.
Define version constraint on composer-plugin.
Fix code style issues.
Drop support for Contao 2.11.
Fix whitelist in phpunit.xml.dist.
Do not add namespace in bootstrap.php.
Fix author annotation.
Move event registration to event_listeners.php.
Fix phpmd issues.
Fix authors again.
Add sudo: false to .travis.yml.
Apply the git-depth hack to make travis happy again.
Reindent .travis.yml.
Fix event_listeners.php - array notation was missing.