Fill in release date for 2.6.1

Fill in release date for 2.6

Fill in release date for 2.5.2

Version bump to 2.6rc1

Fill in release date for 2.5.1

Version bump to 2.5 final

Version bump to 2.5rc1

Document extended LTS date of Wagtail 1.13

Generate new source strings for translation

Fill in release date for 2.3