## Bug description

We've had a user create a funnel with Korean characters and 17 steps, which causes this issue:
![image](https://user-images.githubusercontent.com/1727427/120301818-8c212a00-c2cd-11eb-8b00-7ba242e4a9ab.png)

## Expected behavior

We should send requests to api/insight/funnel using POST instead of GET.

## How to reproduce

1.
2.
3.

## Environment

- [ ] PostHog Cloud
- [ ] self-hosted PostHog, version/commit: _please provide_

## Additional context



#### *Thank you* for your bug report – we love squashing them!

posthog/utils.py
try:
        return datetime.datetime.strptime(input, "%Y-%m-%d").replace(tzinfo=pytz.UTC)
    except ValueError:
        pass
    
    
    try:
        return parser.isoparse(input).replace(tzinfo=pytz.UTC)
    except ValueError:
        pass
    regex = r"\-?(?P<number>[0-9]+)?(?P<type>[a-z])(?P<position>Start|End)?"
    match = re.search(regex, input)
    date = timezone.now()
    if not match:
        return date
    if match.group("type") == "h":
        date = date - relativedelta(hours=int(match.group("number")))
        return date.replace(minute=0, second=0, microsecond=0)
    elif match.group("type") == "d":
        if match.group("number"):
            date = date - relativedelta(days=int(match.group("number")))
    elif match.group("type") == "m":
        if match.group("number"):
            date = date - relativedelta(months=int(match.group("number")))
        if match.group("position") == "Start":