Add fr Relative Date to TTTTimeIntervalFormatter

Despite FormatterKit.strings being localized in French and setting usesIdiomaticDeicticExpressions to YES I wasn't able to display relative date in french...

I added a method to handle fr but shouldn't we do something like this instead ?
``` objc
- (NSString *)localizedIdiomaticDeicticExpressionForComponents:(NSDateComponents *)components {
    if ([components year] == -1) {
        return NSLocalizedStringFromTable(@"last year", @"FormatterKit", @"");
    } else if ([components month] == -1 && [components year] == 0) {
        return NSLocalizedStringFromTable(@"last month", @"FormatterKit", @"");
    } else if ([components week] == -1 && [components year] == 0 && [components month] == 0) {
        return NSLocalizedStringFromTable(@"last week", @"FormatterKit", @"");
    } else if ([components day] == -1 && [components year] == 0 && [components month] == 0 && [components week] == 0) {
        return NSLocalizedStringFromTable(@"yesterday", @"FormatterKit", @"");
    }
    
    if ([components year] == 1) {
        return NSLocalizedStringFromTable(@"next year", @"FormatterKit", @"");
    } else if ([components month] == 1 && [components year] == 0) {
        return NSLocalizedStringFromTable(@"next month", @"FormatterKit", @"");
    } else if ([components week] == 1 && [components year] == 0 && [components month] == 0) {
        return NSLocalizedStringFromTable(@"next week", @"FormatterKit", @"");
    } else if ([components day] == 1 && [components year] == 0 && [components month] == 0 && [components week] == 0) {
        return NSLocalizedStringFromTable(@"tomorrow", @"FormatterKit", @"");
    }
    
    return nil;
}
```