Allow custom parentNode for hover tooltips

[whazor]

Issue #, if available: n/a

Description of changes:
Just like tooltips, we allow custom parent nodes such that the hover tooltip could also be added to Ace editor instead of document body.

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[codecov]

Codecov Report

Patch coverage: 75.00% and no project coverage change.

Comparison is base (5f2face) 86.94% compared to head (0d5c90e) 86.94%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #5156   +/-   ##
=======================================
  Coverage   86.94%   86.94%           
=======================================
  Files         560      560           
  Lines       44220    44220           
  Branches     6854     6854           
=======================================
  Hits        38446    38446           
  Misses       5774     5774           

Flag	Coverage Δ
unittests	86.94% <75.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/tooltip.js	89.67% <75.00%> (ø)

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