Remove component for starting new round and move logic to service
Since a component in Angular is meant to be a black box and parent components aren't supposed to be aware of its contents, nested material components are not intended. Using nested material components anyway can lead to errors e.g. as mentioned in #1148 (closed).
Also add tooltip to button for starting multiple rounds if disabled again, since changes of !1772 (merged) didn't lead to the a11y error.
Closes #1148 (closed)
Edited by Lukas Weingarten