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.

This reduces the complexity of the reducer, as well as how frequently it's run. The VM will emit a targets update after a step if any target info has changed.

With jscodeshift thank God

* Fix costume loading in sprite info pane

Requires LLK/scratch-vm#517

* Fix costume loading in costumes tab

Requires LLK/scratch-vm#517