Increase TypeScript strictness

Refactor components and services so that noImplicitAny and strictNullChecks can be enabled.

For this many lines have been adjusted so that a comprehensive testing is necessary.

Logic has been adjusted in the following files:

• comment-settings.component.ts
• room-create.component.ts
• abstract-comment-page.component.ts
• room-list.component.ts
• update-info.component.ts
• group-content.component.ts
• control-bar.component.ts
• global-storage.service.ts
• api-config.service.ts
• content-group.service.ts
• content-service.ts
• ws-connector.service.ts

Closes #1171 (closed)