Add possibility to have more than one fallback language

In a current international project we had the requirement to provide multiple languages as a fallback. 
Therefore if the preferred primary language is not present and a fallback language won't match, the new added multi-fallback function iterates through the array.
If no translation can be found for languages in that array, it will have the same behaviour as the existing workflow / function.

The implementation is a derived variant of the existing fallbackLanguage function. 
On the one hand we could also integrate the new functionality directly into that function and then check if the input is an array or just a plain string. 
But for readability and maximum compatibility, I decided to just provide an extra function for the first multilang-fallback stuff.

The languages might be set with 

```
$translateProvider.fallbackLanguages(['de_DE','fr_FR']);...
```

I also reformatted the main testfile a bit to have always the same paranthese style etc.

Comments, remarks and blames welcome ;-)

Greets,

Thorsten