refactor: change default isochrone color & enable alternative colors

- switching to qgis plugin color scheme as default
- use higher default opacity for better visibility
- loading default colors from config file to make them customizable
- enable red-blue color scheme as alternative colors in settings
- remove unused html-colors package

docs/en-translation-source-merged.json

@@ -362,7 +362,7 @@
     "areaUnit": "Area unit",
     "saveToLocalStorage": "Save in my browser",
     "routeInstructions": "Routing instructions",
-    "randomizedIsochroneColors": "Randomized isochrone colors",
+    "alternativeIsochroneColors": "Randomized isochrone colors",
     "distanceMarkers": "Distance markers",
     "elevationProfile": "Elevation profile",
     "mapSettings": "Map view and extra information",

package.json

@@ -57,7 +57,6 @@
     "eslint-loader": "^4.0.2",
     "eslint-plugin-cypress": "^2.12.1",
     "eslint-plugin-vue": "^7.0.0-beta.2",
-    "html-colors": "0.0.4",
     "html-webpack-plugin": "^5.0.0",
     "leaflet": "^1.8.0",
     "leaflet-draw-locales": "^1.1.0",