region: Use correct icon for the drag handle

There's a dedicated icon for drag handles - we should make use of
it. Also, change the color of the handle so it looks like it is
part of the row.

Fixes #590
Status Job ID Name Coverage
  Build
passed #357646
build

00:02:59

 
  Test
passed #357648
asan

00:03:29

passed #357647
test

00:01:41

 
  Manual
manual #357653
allowed to fail manual
armv8
manual #357649
allowed to fail manual
flatpak
manual #357652
allowed to fail manual
msan
manual #357654
allowed to fail manual
ppc64le
manual #357650
allowed to fail manual
tsan
manual #357651
allowed to fail manual
ubsan
 
  Review
manual #357655
allowed to fail manual
review
manual #357656
allowed to fail manual
stop_review