Refactor code to comply with ESLint rules

Major refactoring using ESLint with rules from AirBnb and Vue.

Enable most of the ESLint rules and do necessary linting in the code.
Also add more information for rules that are disabled to describe what
they are and why they are disabled.

Allow logging (`console.log`) in test files, and in development mode
(e.g. when working with `npm run serve`), but disable it when
environment is production (as pre-configured by Vue). Also add flag
(`--mode production`) in `lint:eslint` command so production linting is
executed earlier in lifecycle.

Disable rules that requires a separate work. Such as ESLint rules that
are broken in TypeScript: no-useless-constructor (eslint/eslint#14118)
and no-shadow (eslint/eslint#13014).

src/presentation/components/TheFooter/DownloadUrlListItem.vue

@@ -2,14 +2,16 @@
   <span class="url">
     <a :href="downloadUrl"
         v-bind:class="{
-            'url__active': hasCurrentOsDesktopVersion && isCurrentOs,
-            'url__inactive': hasCurrentOsDesktopVersion && !isCurrentOs,
-            }">{{ operatingSystemName }}</a>
+        'url__active': hasCurrentOsDesktopVersion && isCurrentOs,
+        'url__inactive': hasCurrentOsDesktopVersion && !isCurrentOs,
+      }">{{ operatingSystemName }}</a>
   </span>
 </template>
 
 <script lang="ts">
-import { Component, Prop, Watch, Vue } from 'vue-property-decorator';
+import {
+  Component, Prop, Watch, Vue,
+} from 'vue-property-decorator';
 import { Environment } from '@/application/Environment/Environment';
 import { OperatingSystem } from '@/domain/OperatingSystem';
 import { ApplicationFactory } from '@/application/ApplicationFactory';
@@ -18,58 +20,61 @@ import { ApplicationFactory } from '@/application/ApplicationFactory';
 export default class DownloadUrlListItem extends Vue {
   @Prop() public operatingSystem!: OperatingSystem;
 
-  public downloadUrl: string = '';
-  public operatingSystemName: string = '';
-  public isCurrentOs: boolean = false;
-  public hasCurrentOsDesktopVersion: boolean = false;
+  public downloadUrl = '';
+
+  public operatingSystemName = '';
+
+  public isCurrentOs = false;
+
+  public hasCurrentOsDesktopVersion = false;
 
   public async mounted() {
-      await this.onOperatingSystemChanged(this.operatingSystem);
+    await this.onOperatingSystemChanged(this.operatingSystem);
   }
 
   @Watch('operatingSystem')
   public async onOperatingSystemChanged(os: OperatingSystem) {
     const currentOs = Environment.CurrentEnvironment.os;
     this.isCurrentOs = os === currentOs;
-    this.downloadUrl = await this.getDownloadUrl(os);
+    this.downloadUrl = await getDownloadUrl(os);
     this.operatingSystemName = getOperatingSystemName(os);
     this.hasCurrentOsDesktopVersion = hasDesktopVersion(currentOs);
   }
+}
 
-  private async getDownloadUrl(os: OperatingSystem): Promise<string> {
-    const context = await ApplicationFactory.Current.getApp();
-    return context.info.getDownloadUrl(os);
-  }
+async function getDownloadUrl(os: OperatingSystem): Promise<string> {
+  const context = await ApplicationFactory.Current.getApp();
+  return context.info.getDownloadUrl(os);
 }
 
 function hasDesktopVersion(os: OperatingSystem): boolean {
-    return os === OperatingSystem.Windows
-        || os === OperatingSystem.Linux
-        || os === OperatingSystem.macOS;
+  return os === OperatingSystem.Windows
+    || os === OperatingSystem.Linux
+    || os === OperatingSystem.macOS;
 }
 
 function getOperatingSystemName(os: OperatingSystem): string {
-    switch (os) {
-        case OperatingSystem.Linux:
-            return 'Linux';
-        case OperatingSystem.macOS:
-            return 'macOS';
-        case OperatingSystem.Windows:
-            return 'Windows';
-        default:
-            throw new Error(`Unsupported os: ${OperatingSystem[os]}`);
-    }
+  switch (os) {
+    case OperatingSystem.Linux:
+      return 'Linux';
+    case OperatingSystem.macOS:
+      return 'macOS';
+    case OperatingSystem.Windows:
+      return 'Windows';
+    default:
+      throw new Error(`Unsupported os: ${OperatingSystem[os]}`);
+  }
 }
 
 </script>
 
 <style scoped lang="scss">
 .url {
-    &__active {
-        font-size: 1em;
-    }
-    &__inactive {
-        font-size: 0.70em;
-    }
+  &__active {
+      font-size: 1em;
+  }
+  &__inactive {
+      font-size: 0.70em;
+  }
 }
 </style>