added handlers for prev/next + customizable view for selected days

[SolutiLyon]

Usage example :

const prevHandler = (mom) => {
    // Disable prev if previous month < today
    const prevEnabled = mom.diff(moment(), 'months', true) >= 0;

    this.setState({
        prevEnabled,
        currentMonth: prevEnabled ? mom : moment()
    });
    return prevEnabled;
};

const nextHandler = (mom) => {
    // Always enable next
    const prevEnabled = true;

    this.setState({
        prevEnabled,
        currentMonth: mom
    });
    return true;
};

const getDayView = (date, isWeekend, isSelected, isToday, event, caption) => {
    console.log("DIFF", date.diff(moment(), "days"));

    // Custom view for selected day
    if (isSelected) {
        return (
            <View style={styles.daySelected}>
                <View style={styles.daySelectedContent}>
                    <Text style={styles.daySelectedText}>{caption}</Text>
                </View>
            </View>
        );
    }

    // Opacity to 0.5 for days before today
    return (
        <Text style={{...styles.dayText, opacity: date.diff(moment(), "days") < 0 ? 0.5 : 1}}>{caption}</Text>
    );
};

<Calendar  ...
    viewForDay={getDayView}
    onTouchPrev={prevHandler}
    onTouchNext={nextHandler}
/>