Remove gulp appdmg

[haslinghuis]

• removes gulpfile.js gulp-appdmg.js from linting
• removes gulpefile.js from CI caching
• removes legacy NWjs building from Readme

[netlify[bot]]

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[sonarcloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

See analysis details on SonarCloud