warn: Remove old Article Feedback warning templates

Per request at WT:TW
warn: Work around an apparent iPhone bug

Reported at WT:TW. It seems that the long entries get truncated if
they're not in an optgroup (yes, go figure...)
warn: Correct grammar in edit summary

Per request at WT:TW
arv: Make checkboxes optional; add shared-use checkbox

Per request/discussion at WT:TW.
Merge remote-tracking branch 'azatoth/master'

Conflicts:
	modules/twinklearv.js
	modules/twinklewarn.js
morebits: reverted 19690a8 as per usage in speedy module

Also cherry-picked 9f11520.