Adding support for download and install of .zip addons

Minor UI alteration, and some small changes based on Sybren's feedback

package_manager/__init__.py

@@ -56,8 +56,8 @@ class PackageManagerAddon(bpy.types.PropertyGroup):
     blender = StringProperty()
     warning = StringProperty()
     support = StringProperty()
-    filename = StringProperty()
     module_name = StringProperty()
+    download_url = StringProperty()
 
 class PackageManagerPreferences(AddonPreferences):
     # this must match the addon name, use '__package__'
@@ -81,18 +81,17 @@ class PackageManagerPreferences(AddonPreferences):
         # Display selected add-on
         addon = self.pm_addons[self.pm_addons_index]
         
-        installed = False
-        for module in addon_utils.modules():
-            if module.__name__ == addon.module_name:
-                installed = True
-                break
+        installed = any(module.__name__ == addon.module_name for module in addon_utils.modules())
         
         col_box = layout.column()
         box = col_box.box()
         colsub = box.column()
         
         split = colsub.row().split(percentage=0.25)
-        split.label(text="Installed: %s" % ("Yes" if installed else "No"))
+        if installed and addon.version is not None:
+            split.label(text="Installed: Yes, v%s" % addon.version)
+        else:
+            split.label(text="Installed: No")
         split.separator()
         split.separator()
         split.operator("wm.addon_download_install",