v4: Rename .label class to .tag

Created by: ameya-pandilwar

Renamed the .label class to .tag so as to avoid naming conflict between Bootstrap's '.label' class name and the '' HTML tag. Fix for #19094 (closed)

changed title from Rename .label class to .tag to v4: Rename .label class to .tag

added css v4 labels

changed milestone to %v4.0.0-alpha.3

closed