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

❌ Patch coverage is 81.25000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 77.50%. Comparing base (15564dc) to head (6e8332e).
⚠️ Report is 4 commits behind head on master.

Files with missing lines	Patch %	Lines
src/QueryTemplate.php	81.25%	3 Missing ⚠️

Additional details and impacted files

@@             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     

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[szepeviktor]

@gmazzap friendly ping :)