Replacement pane apply layout

[philippjfr]

Fixes #622

[codecov]

Codecov Report

Merging #971 into master will increase coverage by 0.08%.
The diff coverage is 97.91%.

@@            Coverage Diff             @@
##           master     #971      +/-   ##
==========================================
+ Coverage   85.61%   85.69%   +0.08%     
==========================================
  Files          98       98              
  Lines       10996    11030      +34     
==========================================
+ Hits         9414     9452      +38     
+ Misses       1582     1578       -4

Impacted Files	Coverage Δ
panel/pane/base.py	91.53% <100%> (+1.37%)	⬆️
panel/tests/test_layout.py	100% <100%> (ø)	⬆️
panel/layout.py	83.13% <75%> (-0.01%)	⬇️
panel/depends.py	100% <0%> (+9.09%)	⬆️

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