drop any default required version for EUMM
AutoVersion: lazy loading of DateTime

The AutoVersion plugin now loads DateTime only when needed. This will
reduce the amount of code compiled during `dzil listdeps`.

DateTime 0.44 is added explicitely in dist.ini.
TODO: AutoVersion should declare DateTime 0.44 as a 'develop' prereq.
NextRelease: lazy load DateTime
changelog entry for DateTime lazy load
fix incorrect "added_by" in file objects (github#284)

calculate 'added_by' string immediately, on object creation, and add
additional information to this attribute to track change information.