Merge branch '17-content-creation-datenhaltung' into 'master'

Resolve "content creation - Datenhaltung"

Closes #17

See merge request swtp-block-ws17/arsnova-angular-frontend!29

src/app/answer-option.ts

+export class AnswerOption {
+  label: string;
+  points: string;
+}

src/app/choice-answer.ts

+export class ChoiceAnswer {
+  id: string;
+  revision: string;
+  contentId: string;
+  round: number;
+  selectedChoiceIndexes: number[];
+}

src/app/choice-content.ts

+import { AnswerOption } from './answer-option';
+
+export class ChoiceContent {
+  options: AnswerOption[];
+  correctOtionIndexes: number[];
+  multiple: boolean;
+}

src/app/content.ts

+enum Format {
+  CHOICE,
+  BINARY,
+  SCALE,
+  NUMBER,
+  TEXT,
+  GRID
+}
+
+export class Content {
+  id: string;
+  revision: string;
+  roomId: string;
+  subject: string;
+  body: string;
+  round: number;
+  format: Format;
+  formatAttributes: Map<string, string>;
+}
+

src/app/test-answer.ts

+export class TestAnswer {
+  id: string;
+  revision: string;
+  contendId: string;
+  round: number;
+  subject: string;
+  body: string;
+  read: string;
+  creationTimestamp: Date;
+}