Add rotation of subpixel anti-alias

On GitHub, user monte-monte contributed this code snippet to rotate the
subpixel anti-alias order. Without this, there will be color borders
around text on a rotated screen.
Fix typo in comment
Merge branch 'master' into feature/subpixel-aa
Refactoring; Subpixel AA only if no external

The subpixel anti-alias order is only changed if there is no external
output attached. That way, it does not create color borders on an
external screen, just the internal one.

In order to avoid replication of the external output finding logic, that
was put into another library file.
Remove empty line
Changelog entry