Fix security issues

• Upgrade lint-staged 3d2f80c
• Upgrade Nyc 03d0aff
• Upgrade babel-plugin-istanbul 155e8cb
• Upgrade handlebars from 4.1.2 to 4.5.3 5599815
• Upgrade mixin-deep from 1.3.1 to 1.3.2 8e14d74
• Upgrade Lint-staged containing vulnerabilities in dependencies 801dd1c
• Upgrade @babel/cli containing vulnerabilities in dependencies f6b8eac
• Upgrade @babel/preset-env to get latest browserslist 51e34fb

Update Lodash

Update Lodash (previous version containing security issue)

Fix repeating selector removing definitions

Fix of repeating selectors removing selector's all previous CSS-attributes and update tests

Replace clean-css with more simple implementation

Replace clean-css with more simple implementation. Clean-css is not behaving nice when run on dev-runtime.