Lots of style fixes

• Load the selected theme as fast as possible
• Removed the fade animation on devices < 1000px to increase rendering performance. This should remove the lags when opening a splashscreen on a mobile device
• The error splashscreen now has a red background color
• Fix style issues in the dark theme
• Fixes a bug where the user could not join a session with a clean localstorage
• Default theme is now the dark theme
• The quiz summary will not list the isCorrect value of survey questions anymore
• If the owner of the quiz uses the theme manager in an active quiz there will be no footer icons. The back button will take him back to the quiz lobby

Fixes #276 (closed)