Add support for casadi to solve nonlinear MPCs

Signed-off-by: Austin Schuh <austin.linux@gmail.com>
Change-Id: I5bbdf1aee2a079866145226daf97f68162008dd6
diff --git a/tools/python/requirements.txt b/tools/python/requirements.txt
index 81d306d..086b138 100644
--- a/tools/python/requirements.txt
+++ b/tools/python/requirements.txt
@@ -23,3 +23,5 @@
 
 bokeh
 tabulate
+
+casadi