fixes for the debug report

[quentin]

• update highlightjs and diff2html
• fix: display graphs as images instead of text
• fix: display diffs correctly
• fix: highlight souffle and RAM diffs correctly

[codecov]

Codecov Report

Merging #2433 (7a7381a) into master (2914f7b) will increase coverage by 0.12%.
Report is 17 commits behind head on master.
The diff coverage is 69.25%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2433      +/-   ##
==========================================
+ Coverage   77.75%   77.87%   +0.12%     
==========================================
  Files         474      479       +5     
  Lines       31164    31443     +279     
==========================================
+ Hits        24232    24487     +255     
- Misses       6932     6956      +24     

Files	Coverage Δ
src/FunctorOps.cpp	60.81% <ø> (ø)
src/ast/IterationCounter.cpp	100.00% <100.00%> (ø)
src/ast/QualifiedName.h	94.11% <ø> (ø)
src/ast/Relation.h	100.00% <100.00%> (ø)
src/ast/Term.h	75.00% <100.00%> (-15.00%)	⬇️
src/ast/analysis/PrecedenceGraph.cpp	42.85% <100.00%> (+7.72%)	⬆️
src/ast/analysis/PrecedenceGraph.h	100.00% <ø> (ø)
src/ast/analysis/typesystem/Type.h	50.00% <ø> (ø)
...ast/analysis/typesystem/TypeConstrainsAnalysis.cpp	99.39% <100.00%> (+0.01%)	⬆️
...c/ast/analysis/typesystem/TypeConstrainsAnalysis.h	100.00% <ø> (ø)
... and 42 more

... and 7 files with indirect coverage changes