Also some conversion to new imm mode (T49043).
Multiple editors affected.
We could push this even further & draw all keyframes in an editor with a single draw call.
Something is strange with keyframe markers in blender2.8 -- they're not showing up before or after this commit. They do appear in master. This commit probably needs some follow-up work after keyframes are showing again. Better to share this code now instead of sitting on it.
bbc31e8929