Stop hardcoding "past three versions" in changelog code

[psvenk]

The changelog in the info tab is hardcoded to show release notes for the three¹ most recent versions of Aspine. Instead of doing this, we should show all release notes going back to the earliest patch level of the current version. For example, on version 2.6.4, the release notes going back to 2.6.0 should be shown.

¹ This was originally 2, but I changed it to 3 in 8f037c8 so that the release notes for 2.6.2 are shown in 2.6.4 (because 2.6.1 was the previous version to go on the production server, and 2.6.2 and 2.6.3 are much more notable than 2.6.4).