feat(listview): add method to append multiple items

[TomJGooding]

Closes #2997 by adding a ListView.extend method to append multiple items. This is essentially a cut-and-paste from the existing append method!

Please review the following checklist.

• Docstrings on all new or modified functions / classes
• Updated documentation
• Updated CHANGELOG.md (where appropriate)

[willmcgugan]

LGTM

[TomJGooding]

Thanks! Looks like the changelog has become a bit out of sync, do you want me to submit new PR or will you do this housekeeping before the next release?

[EDIT: Created a quick PR to correct this.]