Resolve "login screen - project setup"

Closes #21

See merge request swtp-block-ws17/arsnova-angular-frontend!3

Added 'check-module' to 'whitespace' configuration to force spaces in import and export statements.

Generated angular project 'arsnova-angular-frontend' by angular cli.

add use-case-diagram

See merge request swtp-block-ws17/arsnova-angular-frontend!2

Update domain model to use different answer types

See merge request swtp-block-ws17/arsnova-angular-frontend!1