Add support for bokeh theme

[brl0]

No description provided.

[codecov]

Codecov Report

Merging #2164 (c57c737) into master (e8f3324) will decrease coverage by 0.00%.
The diff coverage is 75.00%.

@@            Coverage Diff             @@
##           master    #2164      +/-   ##
==========================================
- Coverage   83.82%   83.82%   -0.01%     
==========================================
  Files         182      182              
  Lines       21773    21777       +4     
==========================================
+ Hits        18252    18255       +3     
- Misses       3521     3522       +1     

Impacted Files	Coverage Δ
panel/pane/plot.py	56.98% <75.00%> (+0.39%)	⬆️

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[philippjfr]

Thanks, small comment, otherwise happy with this. If you could also update the documentation in examples/references/panes/Bokeh.ipynb that would be super but I won't let it hold up merging.