Add 'releaseDate' property and sort release notes by it instead of object number

Currently, Release Notes are sorted by object order (ExtensionVersionClass object order). This is very cumbersome to work with, since, if you got something right, you can`t rearrange the order of objects unless if you remove them all and add them back, one by one.

A 'releaseDate' field is more than appropriate, if not required, and I guess it can be extracted from maven metadata as well (for imported versions).