Simplify QueryTemplate::applyFilter()

[szepeviktor]

After trying to understand this method, I'm sorry to report but my 🧠 brain hurt.

This PR makes it easy to understand and maintain. Please see decreasing Complexity below.

[codecov-commenter]

Codecov Report

Merging #28 (6e8332e) into master (15564dc) will decrease coverage by 0.63%.
The diff coverage is 81.25%.

@@             Coverage Diff              @@
##             master      #28      +/-   ##
============================================
- Coverage     78.13%   77.50%   -0.64%     
+ Complexity      230      227       -3     
============================================
  Files            30       30              
  Lines           439      440       +1     
============================================
- Hits            343      341       -2     
- Misses           96       99       +3     

Impacted Files	Coverage Δ
src/QueryTemplate.php	90.69% <81.25%> (-6.93%)	⬇️

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[szepeviktor]

@gmazzap friendly ping :)