Change header for exports

Closes #143

See merge request arsnova/frag.jetzt!156

Change color of comment freeze button

Closes #152

See merge request arsnova/frag.jetzt!154

Make cookie-dialog scrollable

Closes #147

See merge request arsnova/frag.jetzt!152

Login after session creation dialog is accepted

Closes #162

See merge request arsnova/frag.jetzt!153

Make several dialogs scrollable

Closes #147

See merge request arsnova/frag.jetzt!151

Merge branch '161-after-entering-the-session-code-open-the-question-creation-dialog-directly' into 'master'

Open 'create-question'-dialog directly after joining a session

Closes #161

See merge request arsnova/frag.jetzt!150

Merge branch '160-do-not-show-the-registration-form-but-let-the-session-creator-continue-as-a-guest' into 'master'

Resolve "Do not show the registration form, but let the session creator continue as a guest."

Closes #160

See merge request arsnova/frag.jetzt!149

Added fullscreen to toggle button

Closes #150

See merge request arsnova/frag.jetzt!148