Implement PeriodicCallback

[philippjfr]

No description provided.

[codecov-io]

Codecov Report

Merging #348 into master will decrease coverage by 0.23%.
The diff coverage is 31.25%.

@@            Coverage Diff             @@
##           master     #348      +/-   ##
==========================================
- Coverage   87.05%   86.81%   -0.24%     
==========================================
  Files          88       89       +1     
  Lines        7741     8071     +330     
==========================================
+ Hits         6739     7007     +268     
- Misses       1002     1064      +62

Impacted Files	Coverage Δ
panel/callbacks.py	30.95% <30.95%> (ø)
panel/viewable.py	82.62% <33.33%> (-1.08%)	⬇️
panel/pane/vtk.py	27.89% <0%> (-2.93%)	⬇️
panel/param.py	91.21% <0%> (-1.01%)	⬇️
panel/links.py	88.34% <0%> (+3.6%)	⬆️
panel/layout.py	91.95% <0%> (+4.37%)	⬆️

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