Add support for param.Event

[philippjfr]

No description provided.

[codecov]

Codecov Report

Merging #1600 into master will decrease coverage by 0.17%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1600      +/-   ##
==========================================
- Coverage   85.68%   85.50%   -0.18%     
==========================================
  Files         147      147              
  Lines       16460    16644     +184     
==========================================
+ Hits        14104    14232     +128     
- Misses       2356     2412      +56     

Impacted Files	Coverage Δ
panel/param.py	89.97% <ø> (-0.92%)	⬇️
panel/auth.py	38.99% <0.00%> (+4.75%)	⬆️
panel/io/server.py	74.57% <0.00%> (+8.06%)	⬆️

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[philippjfr]

Gonna merge this assuming Event will be merged in some form.