Resolve "participant home screen - room logic"

Closes #42 (closed)

Proposed changes

• Added back button to participant-room view
• Added room logic so that the participant-room view displays current-room information instead of test data
• Added loading-spinner and error page for unavailable room

For testing

• Login as participant, join a room and check if you see the correct room-informations
• Click on the 'back'-button should go back to the participant-home-screen view
• By entering route to not existing room the app should show an error

src/app/participant-room/participant-room.component.ts

@@ -13,14 +13,6 @@ export class ParticipantRoomComponent implements OnInit {
 
   room: Room;
 
-  roomId = '12 34 56 78';
-  roomName = 'Test Room';
-  roomDescription = 'Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore ' +
-    'magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea ' +
-    'takimata sanctus est Lorem ipsum dolor sit amet. Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod ' +
-    'tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea ' +
-    'rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.';
-
   constructor(private location: Location,
               private roomService: RoomService,
               private route: ActivatedRoute) {