Add more info on session resource & getOne domain method

[ronan-gloo]

Reason for this PR

• We need to completely implement the /me resource in order to get info internally
• The domain resource does not provides direct acres to identified resource

Added

• SessionResource::getId() : provides the account id associated to the token
• SessionResource::getRoles() : provides an array of named roles associated to the token
• SessionResource::getLanguageTag() : provides the language tag associate to the token
• AbstractDomainResource::getOne($id) : allow to directly get a resource for the domain
• HalLink::withAddedHref(string $path) : Allow to creates new instance of link with concatenated path

Bug fixes

• InventoryDomain::getByReference() was not checking for NULL resource