Set axis background to transparent in inlinebackend

Fixes #5727, related to #4608

Author: Carreau

config.py

@@ -53,6 +53,7 @@ def _config_changed(self, name, old, new):
         # play nicely with white background in the Qt and notebook frontend
         'figure.facecolor': (1,1,1,0),
         'figure.edgecolor': (1,1,1,0),
+        'axes.facecolor': (1,1,1,0),
         # 12pt labels get cutoff on 6x4 logplots, so use 10pt.
         'font.size': 10,
         # 72 dpi matches SVG/qtconsole