i18n: use TG2 compatible settings names i18n.lang and i18n.enabled Following changes are made: - Remove list of available translations: severely outdated and hard to maintain. - Replace lang with i18n.lang, reasons: - Follow TurboGears2 conventions - Align with 'i18n.enabled' which cannot be shortened - Scoped settings provide grouping and are more clear The old 'lang' is still recognized though, so no upgrade issue. - Introduce/document i18n.enabled Comments are intentionally kept concise in favor of the documentation.