Fix .gdraw rendering

 * Google Drawings (.gdraw) files were being exported by the Unoconv
   exporter.  This was broken (unoconv couldn't handle them) and
   unnecessary, since .gdraws are automatically exported to .jpgs on
   download.  Switching them to be exported by the image renderer lets
   them render successfully and allows MFR to enforce size restrictions
   on the displayed file.

   [SVCS-38]

   Fixes #247

Author: Johnetordoff

setup.py

@@ -42,7 +42,7 @@ def parse_requirements(requirements):
         ],
         'mfr.exporters': [
             # google docs
-            '.gdraw = mfr.extensions.unoconv:UnoconvExporter',
+            '.gdraw = mfr.extensions.image:ImageExporter',
             '.gdoc = mfr.extensions.unoconv:UnoconvExporter',
             '.gsheet = mfr.extensions.unoconv:UnoconvExporter',
             '.gslides = mfr.extensions.unoconv:UnoconvExporter',