Resolve "Content Types"

Closes #159

See merge request swtp-block-ws17/arsnova-angular-frontend!107

Resolve "Content List"

Closes #172

See merge request swtp-block-ws17/arsnova-angular-frontend!112

Change dummy data with correctOptionIndexes, fix error if dialog is closed without the use of buttons

Implement content backup logic, so you can recover by clicking abort when you made content changes in edit-dialog

Fix bug to submit multiple choice content, with more as one true answer, Remove notification when participant sends answer - mat-chip is enough information, Put checkbox's name in a new line

Shrink code, bugfix logic in creator's multiple choice content, add $event to all "button"-methods to prevent problems if it is interpreted as submit, add console.log in submit-method for testing, add reset-method to set all values to default after submit