refactor result classes and code which stores/loads results from storage
diff --git a/wally/report.py b/wally/report.py
index 58dcf56..cf1289b 100644
--- a/wally/report.py
+++ b/wally/report.py
@@ -5,10 +5,13 @@
 import numpy
 import scipy
 import matplotlib
+
+# have to be before pyplot import to avoid tkinter(default graph frontend) import error
+matplotlib.use('svg')
+
 import matplotlib.pyplot as plt
 
 
-matplotlib.use('svg')
 
 
 from .utils import ssize2b