Upgrade flags dependency (#87)

[nico2che]

Close #87

• migrate flag-icon-css to flag-icons
• add copy-svg script to only get used flags from languages.json
• use new flags (es-ct and es-pv)
• minify svgs during build

[VincentLanglet]

Il y a également un test unitaire

languages/tests/languages.test.js

Lines 31 to 38 in 9a2be26

	test('All flag codes exist', () => {
	const countryFlagCodes = languages.map((language) => language.country_flag_code);
	(new Set(countryFlagCodes)).forEach(function (countryFlagCode) {
	expect(fs.existsSync(`${__dirname}/../images/1x1/${countryFlagCode}.svg`)).toBe(true);
	expect(fs.existsSync(`${__dirname}/../images/4x3/${countryFlagCode}.svg`)).toBe(true);
	})
	});

Mais ça fait pas de mal de le checker dans le script 👍