Accented characters are displayed at the end of the list instead of after the non-accented character

The expected behaviour:

• group "a" with "à", "â", etc.
• group "e" with "é", "è", etc

There was 2 problems:

1. the API used to return a wrong sorting - It has been fixed (will soon be merged): haskell-gargantext#331 (closed)
2. the frontend is still displaying a wrong grouping - have to be fixed here