Increase default bleed size to 36 pixels

This results in bleed spacing of ~6mm between each card, and this is
better for cutting, especially with guided cutting systems like the
SureCut.

card_grid_generator/card_grid_generator_extension.py

@@ -47,7 +47,7 @@ class CardGridGenerator(Extension):
         layout.addLayout(row1)
 
         # Bleed dimension row. Also, guides or cropmarks selection.
-        self.bleedInput = QLineEdit('24')
+        self.bleedInput = QLineEdit('36')
         self.guidesCheck = QCheckBox('Guides')
         self.guidesCheck.setChecked(True)
         self.cropmarksCheck = QCheckBox('Cropmarks')