Specifying `widgets` or `widget_location` changes return type from holoviews to panel

#### ALL software version info
hvplot 0.6
holoviews 1.13.5
bokeh 2.2.3

#### Description of expected behavior and the observed behavior
using default widgets seems to return a `holoviews.core.spaces.DynamicMap`, but specifying keywords `widget_location` or `widgets` returns `panel.layout.base.Column` (or Row). This leads to confusing errors when trying to compose elements or link streams. I imagine there are workarounds to get at the DynamicMap embedded within the panel layout, but I'm having trouble figuring it out.

#### Complete, minimal, self-contained example code that reproduces the issue

```python
#minimal reproducible example
import xarray as xr
import hvplot.xarray
import holoviews as hv
from holoviews.streams import RangeXY

air_ds = xr.tutorial.open_dataset('air_temperature').load()
air = air_ds.air
print(type(air.hvplot.image()))
print(type(air.hvplot.image(widget_location='bottom')))
#
#
```

##### bug1 composing elements
```python
img = air.hvplot.image(widget_location='bottom')
point = hv.Points([(260, 40)])
img * point
```

```pytb
---------------------------------------------------------------------------
TypeError Traceback (most recent call last)
in
2 img = air.hvplot.image(widget_location='bottom')
3 point = hv.Points([(260, 40)])
----> 4 img * point

TypeError: unsupported operand type(s) for *: 'Column' and 'Points'
```

##### bug2 adding a stream
```python
# bug 2 adding stream
img = air.hvplot.image(widget_location='bottom')
range_xy_stream = RangeXY(source=img)
img
```

```pytb
/srv/conda/envs/notebook/lib/python3.8/site-packages/holoviews/plotting/plot.py in (.0)
953 streams = [
954 s for src, streams in registry for s in streams
--> 955 if src is source or (src._plot_id is not None and
956 src._plot_id == source._plot_id)]
957 cb_classes |= {(callbacks[type(stream)], stream) for stream in streams

AttributeError: 'Column' object has no attribute '_plot_id'
```

@jbednar or @philippjfr , it would be great to have an example of how to work around these issues by accessing the DynamicMap wrapped in panel.