MBS-9106: Fix overflow mootimeter with the footer in fullscreen mode

[tholudwig]

Description
In fullscreen mode, the Mootimeter panel can protrude beyond the footer, especially with long surveys or quizzes. This affects both our theme_mebis and, albeit to a lesser extent, theme_boost.

The problem does not exist in the normal view, as the panel is scrollable here.

**Goal

1. even in fullscreen mode, the panel does not cover the footer.
2. the solution works for all designs.
3. open: should the panel be scrollable in fullscreen or does the entire mootimetre area grow accordingly?
4. solution does not change the normal mode.

Test instructions

1. create Mootimeter activity with quiz.
2. add many possible answers.
3. switch to full screen

• Before patch: Panel protrudes into the footer
• after the patch: panel no longer protrudes into the footer in both theme_mebis and theme_boost

4. deactivate fullscreen

• Both solutions do not differ