Replace module mocks with alternative methods

assets/karma.conf.js

assets/package-lock.json

assets/package.json

assets/rollup.config.js

assets/src/scripts/components/hydrograph/index.spec.js

assets/src/scripts/components/hydrograph/layout.spec.js

assets/src/scripts/components/hydrograph/legend.js

assets/src/scripts/components/hydrograph/tooltip.spec.js

assets/src/scripts/components/map/index.js

assets/src/scripts/components/map/index.spec.js

assets/src/scripts/components/map/legend.js

assets/src/scripts/components/map/legend.spec.js

assets/src/scripts/floodData.js

assets/src/scripts/floodData.spec.js

assets/src/scripts/index.js

assets/src/scripts/index.spec.js

assets/src/scripts/models.js

assets/src/scripts/models.spec.js

assets/src/scripts/statisticsData.js

assets/src/scripts/statisticsData.spec.js