Better messaging for descriptionless modpacks

[HebaruSan]

Problem

If a user creates a modpack without a description, SpaceDock displays this message:

It's wrong in two ways:

1. The user is addressed as if they own the mod pack even if they aren't the creator and could not edit it
2. It suggests that there are no mods added, even if there are several added

Cause

Just sloppiness in the mod_list.html template.

Changes

• Now if you can't edit, the message just says "No description."
• Now if you can edit and there are mods, the message just mentions the description being missing
• Otherwise the current message is shown