Jack/mermaid fixes

[cuminandpaprika]

Fixes # .

Changes proposed in this pull request:

• Add nil check for datamodeldiagram
• Add GeneratePrimitive function for creating datamodel diagrams for primitive types
• Display applications which call specified applications instead of just Visa and MasterCard

Checklist:

• [x] Added related tests
• [x] Made corresponding changes to the documentation

[codecov[bot]]

Codecov Report

Merging #969 into master will increase coverage by 1.15%. The diff coverage is 87.03%.

@@            Coverage Diff             @@
##           master     #969      +/-   ##
==========================================
+ Coverage   83.35%   84.51%   +1.15%     
==========================================
  Files          73       75       +2     
  Lines       10609    10549      -60     
==========================================
+ Hits         8843     8915      +72     
+ Misses       1432     1322     -110     
+ Partials      334      312      -22     

Impacted Files	Coverage Δ
pkg/pbutil/output.go	76.00% <ø> (-0.48%)	:arrow_down:
pkg/syslwrapper/app.go	93.44% <ø> (-0.05%)	:arrow_down:
pkg/syslwrapper/test_helper.go	57.89% <ø> (-1.42%)	:arrow_down:
pkg/importer/importer.go	63.15% <63.15%> (ø)
pkg/mermaid/datamodeldiagram/datamodeldiagram.go	60.00% <64.70%> (+1.42%)	:arrow_up:
pkg/mod/gomod.go	73.68% <66.66%> (+1.27%)	:arrow_up:
pkg/mod/module.go	66.66% <72.72%> (+0.95%)	:arrow_up:
pkg/parse/parse.go	85.34% <73.07%> (+1.37%)	:arrow_up:
...g/mermaid/integrationdiagram/integrationdiagram.go	83.19% <82.45%> (-1.19%)	:arrow_down:
pkg/importer/openapi.go	85.96% <85.18%> (-3.48%)	:arrow_down:
... and 23 more