Must Article 3(1)(a) and (c) of Council Directive 2000/78/EC of 27 November 2000 establishing a general framework for equal treatment in employment and occupation be construed as permitting the exclusion from the scope of Council Directive 2000/78/EC, and consequently also as permitting the exclusion from the application of the sanctions laid down in national law pursuant to Article 17 of Council Directive 2000/78/EC, of the freedom of choice of parties to a contract so long as that choice is not based on sex, race, ethnic origin or nationality, in a situation where the alleged discrimination consists in a refusal to enter into a civil-law contract under which work is to be carried out by a self-employed natural person when that refusal is based on the sexual orientation of the prospective counterparty?