Fix issues with requirejs and templates

[philippjfr]

Some unfortunate workarounds and other miscellaneous fixes. Would like to find a better solution to handling requirejs but for now we add some workarounds that ensure requirejs does not clash with the require/define utilities provided by Ace. Also fixes a few other issues.

[codecov]

Codecov Report

Merging #1472 into master will decrease coverage by 0.01%.
The diff coverage is 73.91%.

@@            Coverage Diff             @@
##           master    #1472      +/-   ##
==========================================
- Coverage   86.20%   86.19%   -0.02%     
==========================================
  Files         139      139              
  Lines       15445    15459      +14     
==========================================
+ Hits        13315    13325      +10     
- Misses       2130     2134       +4     

Impacted Files	Coverage Δ
panel/depends.py	63.63% <0.00%> (ø)
panel/command/serve.py	17.33% <20.00%> (+0.66%)	⬆️
panel/layout/accordion.py	84.72% <66.66%> (-0.79%)	⬇️
panel/io/resources.py	91.83% <100.00%> (-1.19%)	⬇️
panel/io/server.py	62.43% <100.00%> (+0.37%)	⬆️
panel/layout/card.py	95.74% <100.00%> (ø)
panel/layout/grid.py	75.00% <100.00%> (ø)

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