[BUG] Icons are not centered vertically

[macmoritz]

Issue Summary

The two/three buttons, quit, question (and setting), in the top left are not centered correctly.
Also, how about changing the X to X-Circle-Fill to be more consistent?

Expected Behavior

Button labels are centered.

Additional Context

I tried to change it, but I have no experience with LVGL yet.
Currently it seems that the icon font is not centered in it self, but I believe this is the case in the bootstrap font.