allow cost / set-icon to be displayed in body-top ONLY (#258)

previously, if you used, ie, "--cost=body-top", the cost would show in
the tab AND body-top.  Since the help text implies that the way to
accomplish this should be "--cost=tab --cost=body-top" (and because if you
put it in body-top, it's probably because you want to save space on the
tab)

src/domdiv/main.py

@@ -296,19 +296,19 @@ def parse_opts(cmdline_args=None):
         "--cost",
         action="append",
         choices=LOCATION_CHOICES,
-        default=["tab"],
         help="Where to display the card cost; may be set to "
         "'hide' to indicate it should not be displayed, or "
-        "given multiple times to show it in multiple places.",
+        "given multiple times to show it in multiple places. "
+        "(If not given, will default to 'tab'.)",
     )
     group_tab.add_argument(
         "--set-icon",
         action="append",
         choices=LOCATION_CHOICES,
-        default=["tab"],
         help="Where to display the set icon; may be set to "
         "'hide' to indicate it should not be displayed, or "
-        "given multiple times to show it in multiple places.",
+        "given multiple times to show it in multiple places. "
+        "(If not given, will default to 'tab'.)",
     )
     group_tab.add_argument(
         "--no-tab-artwork",
@@ -738,6 +738,12 @@ def clean_opts(options):
         print("** Warning: --tab-serpentine only valid if --tab-number > 2. **")
         options.tab_serpentine = False
 
+    if options.cost is None:
+        options.cost = ["tab"]
+
+    if options.set_icon is None:
+        options.set_icon = ["tab"]
+
     if options.sleeved_thick:
         options.thickness = 3.2
         options.sleeved = True