Add duplicate button. Pass the costume ID to paint (the previous costume ID used matches when duplicate is used.) When switching to the costume tab, open the current costume.

* Implement paint-75: Add blank costume button

* add backdrop icon, use default name

thanks @fsih !

Changed existing string ids to use the convention `<repo>.<component>.<identifier>`

Keep localization in the container level. Ideally we should not be passing message descriptors.

Costumes and Sound tab strings.