Add Warp and Small tile filters again
Warp and Small tiles were removed in b18262cd for unclear reasons, but the filters still exist in GIMP, so let's add them again.
Dialog images are updated for GIMP 3 along with some light styling fixes for text.
Displacement map in Warp no longer has a drop-down, so I call the browse button a file picker
instead. Otherwise quite similar to the versions used in gimp-help 2.8.
Fixes #451 (closed)