refactor: change meta class structure to include types.

Introduce requiredness of translations via implemented interface.

src/core/base/AcademicDegree.ts

@@ -14,6 +14,7 @@
  */
 import {SCThing} from '../Thing';
 import {SCThingMeta} from '../Thing';
+import {SCMetaTranslations} from '../types/i18n';
 
 /**
  * An academic degree without references
@@ -40,19 +41,31 @@ export interface SCAcademicDegreeWithoutReferences extends SCThing {
 export interface SCAcademicDegree extends SCAcademicDegreeWithoutReferences {
 }
 
-export class SCAcademicDegreeMeta extends SCThingMeta {
-  static fieldTranslations = {
-    ...SCThingMeta.fieldTranslations,
+/**
+ * Meta information about academic degrees
+ */
+export class SCAcademicDegreeMeta extends SCThingMeta implements SCMetaTranslations<SCAcademicDegree> {
+  /**
+   * Translations of fields
+   */
+  fieldTranslations = {
     de: {
+      ...SCThingMeta.getInstance().fieldTranslations.de,
       academicDegree: 'Hochschulgrad',
       academicDegreewithField: 'Abschlussbezeichnungen',
       academicDegreewithFieldShort: 'Abschlussbezeichnungen (kurz)',
     },
+    en: {
+      ...SCThingMeta.getInstance().fieldTranslations.en,
+    },
   };
 
-  static fieldValueTranslations = {
-    ...SCThingMeta.fieldValueTranslations,
+  /**
+   * Translations of values of fields
+   */
+  fieldValueTranslations = {
     de: {
+      ...SCThingMeta.getInstance().fieldValueTranslations.de,
       academicDegree: {
         'bachelor': 'Bachelor',
         'diploma': 'Diplom',
@@ -64,6 +77,9 @@ export class SCAcademicDegreeMeta extends SCThingMeta {
         'state examination': 'Staatsexamen',
       },
     },
+    en: {
+      ...SCThingMeta.getInstance().fieldValueTranslations.en,
+    },
   };
 }