KfW GUI -- update expand/collapse icon rendering

Use DrawThemeBackground() to draw the icons from the explorer treeview.

https://github.com/krb5/krb5/commit/28d8e44e3474afcc1ea3b472c3336bd1017b55a6
Author: Kevin Wasserman <kevin.wasserman@painless-security.com>
Committer: Ben Kaduk <kaduk@mit.edu>
Commit: 28d8e44e3474afcc1ea3b472c3336bd1017b55a6
Branch: master
 src/windows/leash/LeashView.cpp |   33 +++++++++++++++++++++++----------
 1 files changed, 23 insertions(+), 10 deletions(-)