#818 Remove mopidy lux from documentation

(cherry picked from commit 06d7d650f870dfe55e02bc091f6f344df2762ef9)
(cherry picked from commit c230a0f64cf48eac18d72dc04827afe88220bcc6)
docs: Add sponsors page

(cherry picked from commit b40409141fe6b8012ff11bb2d9fb041831e02571)
docs: Update changelog
Bump version to 0.19.4
Release v0.19.4