title: Setting default options for hvplots
body: <p>I would like to set default options for the plots generated by hvplots.</p>
  
  <p>Normally in holoviews I would do this to set defaults for every plot:</p>
  
  <pre><code>import holoviews as hv
  from holoviews import opts
  hv.extension('bokeh')
  opts.defaults(opts.Curve( height=400, width=900 ,show_grid=True))
  </code></pre>
  
  <p>Now that I'm using hvplots the import has become the following for xarray based plotting</p>
  
  <pre><code>import xarray as xr
  import hvplot.xarray
  </code></pre>
  
  <p>If I have an xarray dataset and I want to plot one of the dimensions then I use this</p>
  
  <pre><code>ds.myDims.hvplot()
  </code></pre>
  
  <p>However this gives a plot with a default width and no grid lines. To add this I need to specify the options with the plot.</p>
  
  <pre><code>ds.myDims.hvplot(height=400, width=900,grid=True)
  </code></pre>
  
  <p>Ideally I'd like to set the height, width, grid etc globally, like I can in holoviews, so I don't have to specify it for every plot.</p>