UI for editing usual names

[D4rkHeart]

Implement the interface for choosing the usual name for profiles with more than one first/family name.
Interface should make clear that the usual name can only be composed by a subset of the official names.
The user should be addressed to HR for changes concerning his official names.
The usual name will PUT to api.epfl.ch. We already have the access rights but implementation/testing are still missing.