Convert dynamictext to use affine transition.
Convert dynamictext to use affine transition.

This facilitates good quality animation and fixes a compositing bug:
https://forum.shotcut.org/t/shotcut-text-filter-bugs-v18-06-02/5758/5

j-b-m/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,j-b-m/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt,mltframework/mlt,mltframework/mlt,j-b-m/mlt,mltframework/mlt