Document extended LTS date of Wagtail 1.13

Generate new source strings for translation

Fill in release date for 2.3

Version bump to 2.3rc2

Version bump to 2.3rc1

Fill in release date for 2.2.2

Release note for wagtail#4730

Specify Elasticsearch <6.3.1

Version bump to 2.0.2

Version bump to 1.13.4