add UI-testing

[romaninsh]

Implementation of UI testing (see ticket #9). Travis will now emulate browser and run Behat tests while collecting coverage info.

This PR should have significant impact in Coverage %

[codecov]

Codecov Report

Merging #262 into develop will increase coverage by 1.17%.
The diff coverage is 100%.

@@              Coverage Diff              @@
##             develop     #262      +/-   ##
=============================================
+ Coverage      69.84%   71.01%   +1.17%     
  Complexity      1110     1110              
=============================================
  Files             62       62              
  Lines           2729     2729              
=============================================
+ Hits            1906     1938      +32     
+ Misses           823      791      -32

Impacted Files	Coverage Δ	Complexity Δ
src/LoremIpsum.php	77.27% <100%> (ø)	7 <0> (ø)	⬇️
src/jsExpression.php	83.54% <100%> (ø)	36 <0> (ø)	⬇️
src/TableColumn/Status.php	56.25% <0%> (-28.13%)	10% <0%> (ø)
src/View.php	79.68% <0%> (+0.95%)	129% <0%> (ø)	⬇️
src/App.php	77.33% <0%> (+1.77%)	93% <0%> (ø)	⬇️
src/jsCallback.php	75.71% <0%> (+48.57%)	29% <0%> (ø)	⬇️

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