Merge tag '1.2' into develop

Version 1.2
Merge branch 'master' into develop
Require contao/core >=2.11,<4-dev now.
Use PSR1+2 and introduce CI tests.
Add class EventDispatcherEvents, that hold all event names.
Extract complete creation and configuration into a class.

The creation and configuration will now made by the
EventDispatcherInitializer class. This also include a new feature, each
module can add a /config/event_listeners.php and
/config/event_subscribers.php which must return an array of listeners
and subscribers.
Bump branch aliases.
Update readme.
Fix service event-dispatcher.initializer must be a singleton.
Update readme.
Update readme.
Require contao-community-alliance/dependency-container ~1.6.
Add batches to readme.
Add the build matrix and composer install commands.
Merge branch 'release/1.3.0'