This reverts commit ea633f3d.

fixes #3554

incoming direct connections in receive mode wouldn’t clear the entire
destination from the input stream; thus adding a leading 0x00 to the file

fixes #3557

* Use dark navigation bar on dark theme

This approach uses `tools:targetApi` instead of separate theme file and
avoids lint errors.

* Use dark navigation bar in QR scanner activity

This is consistent with the black background that is already used in
that activity.