[partition] Change shortcut for "Create" to 'a'

Untangle the shortcuts; Create and Cancel had an overlap.
Skip 'r' (Revert all changes) and 'e' (Edit) and settle on
'a' (which might also mean "Add").

FIXES #977

src/modules/partition/gui/PartitionPage.ui

@@ -104,7 +104,7 @@
      <item>
       <widget class="QPushButton" name="createButton">
        <property name="text">
-        <string>&amp;Create</string>
+        <string>Cre&amp;ate</string>
        </property>
       </widget>
      </item>