fix/#522 Ajax error display

[ibelar]

This will catch up callback request when exception occur and properly format server response in order to properly handle exception.

fixes #522

[codecov]

Codecov Report

Merging #529 into develop will decrease coverage by 0.03%.
The diff coverage is 0%.

@@              Coverage Diff              @@
##             develop     #529      +/-   ##
=============================================
- Coverage      66.81%   66.77%   -0.04%     
- Complexity      1600     1601       +1     
=============================================
  Files             90       90              
  Lines           3842     3844       +2     
=============================================
  Hits            2567     2567              
- Misses          1275     1277       +2

Impacted Files	Coverage Δ	Complexity Δ
src/App.php	73.75% <0%> (-0.62%)	105 <0> (+1)

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