Revisit Python API

Right now the Python API doesn't feel very pythonic (i.e., OOP) -- it feels more like a port of the R API to Python.

I think we should consider something like this:

```python
# Instead of querychat.init()
qc = QueryChat(data)

# Instead of querychat.sidebar()
qc.sidebar()

# Instead of querychat.server()
qc.server()
``` 
