Add component offering markdown action buttons

Resolve "internationalization"

Closes #160

See merge request swtp-block-ws17/arsnova-angular-frontend!106

Resolve "login/room creator screen bug"

Closes #170

See merge request swtp-block-ws17/arsnova-angular-frontend!105

Add extraction command

Resolve "Feedback Barometer"

Closes #158

See merge request swtp-block-ws17/arsnova-angular-frontend!111

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