Improve source location and context filter

[bkryza]

Fixes #392

[codecov]

Codecov Report

Attention: Patch coverage is 92.05607% with 17 lines in your changes missing coverage. Please review.

Project coverage is 90.20%. Comparing base (09d62c0) to head (2cf1f9d).

Files with missing lines	Patch %	Lines
src/common/model/filters/diagram_filter.h	86.31%	13 Missing ⚠️
src/class_diagram/model/diagram.h	83.33%	2 Missing ⚠️
src/common/model/element.cc	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #393      +/-   ##
==========================================
- Coverage   90.24%   90.20%   -0.05%     
==========================================
  Files         152      152              
  Lines       19033    19134     +101     
==========================================
+ Hits        17176    17259      +83     
- Misses       1857     1875      +18     

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