Fix Django resource handling

[philippjfr]

@sdc50 Before this PR Django wasn't working at all for me since it couldn't load some resources. Did you have similar issues?

[codecov]

Codecov Report

Merging #3116 (998a58a) into master (77882db) will decrease coverage by 0.07%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #3116      +/-   ##
==========================================
- Coverage   83.10%   83.02%   -0.08%     
==========================================
  Files         192      192              
  Lines       25460    25484      +24     
==========================================
  Hits        21159    21159              
- Misses       4301     4325      +24     

Impacted Files	Coverage Δ
panel/io/django.py	0.00% <0.00%> (ø)

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[sdc50]

Did you have similar issues?

I haven't been able to reproduce this issue. For me using both inline and cdn worked at least sense v0.13.0a28.

Note: I haven't been able to get the bokeh resources server option to work for me because of the URL it tries to use.