So using filters like `beautify` won't result in the following error:
```
Traceback (most recent call last):
File "/usr/lib/python3.8/site-packages/urlwatch/handler.py", line 120, in process
data = FilterBase.process(filter_kind, subfilter, self, data)
File "/usr/lib/python3.8/site-packages/urlwatch/filters.py", line 180, in process
return filtercls(state.job, state).filter(data, subfilter)
File "/usr/lib/python3.8/site-packages/urlwatch/filters.py", line 276, in filter
raise ImportError('Please install BeautifulSoup')
ImportError: Please install BeautifulSoup
```