Add dark mode (#33)

Closes: #18

This PR adds dark mode styling and an app setting to choose light, dark, or auto mode.

Reviewed-on: Georgi_Lab/ALVINN_f7#33

src/components/svg-icon.vue

@@ -18,7 +18,7 @@
       },
       fillColor: {
         type: String,
-        default: "#002F65"
+        default: "var(--avn-theme-color)"
       }
     }
   }