Multi language communication

[bjendres]

We would like to expand this extension so it can deal with different languages. For that, we will do two changes:

1. The event message configuration will get a option to determine the requested communication language. This field allows you to select a hierarchy of language sources. Those could be:
   1. a custom field language field with the event object
   2. a custom field language field with the participant object
   3. preferred language of the contact
   4. browser language setting
   5. a fallback default language
2. Each rule will get an additional multi-entry languages filter field, and the rule will only apply if the field is empty, or the desired communication language is listed in the languages.
3. The determined communication language will also be passed to the template as a smarty variable, e.g. if the template is largely the same and you just want to change a couple of words between BE/AE.