mod portal: changelogs

[golfmiketango]

In the mod portal, it would be fantastic if an end-user-facing field were provided for mod authors to publish their changelogs. We had this in the old forum-based mod publishing convention but effectively lost it when we moved to the mod portal.

Ideally, when a mod has turned yellow in the gui, indicating that an update is available, the end-user could immediately read the mod author's corresponding description of what has been changed/fixed/improved, what is likely to happen to his or her campaign as a result of incorporated said changes, whether there are known bugs in the new release, and so forth. This way, end-users could make much more intelligent decisions about when to upgrade mods.