fix of #131, #132, spinner while loading iframe content

[AJIXuMuK]

Q	A
Bug fix?	[x]
New feature?	[ ]
New sample?	[ ]
Related issues?	#131, #132

What's in this Pull Request?

• fix of FieldLookupRenderer: Lookup dialog is empty #131,
• fix of Unnecessary horizontal scroll in IFrame dialog #132,
• IFrameDialog component renders spinner while the content of the iframe is being loaded

[codecov-io]

Codecov Report

Merging #133 into dev will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##              dev     #133   +/-   ##
=======================================
  Coverage   80.63%   80.63%           
=======================================
  Files          10       10           
  Lines         346      346           
  Branches       78       71    -7     
=======================================
  Hits          279      279           
  Misses         44       44           
  Partials       23       23

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[estruyf]

Thanks @AJIXuMuK for this PR it will be available in 1.9.0.