SB2 Import Modal

Asset menu follow ups

I also suspect this will fix some of the times when the menu
mysteriously stayed open, because it was being re-rendered for by
mistake.

Add new asset menu system

This makes it possible to use on iOS/touch

Duplicate costume

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.

Fix deleting in sprite selector item event bubbling

This is required because you can delete the last sound, and without a re
render the tab will continue to render the sound editor, causing an
error.

Improvements to error state: input outline shows with or without focus, and added new error div which shows if there's an error, but goes away if the user starts changing what they had submitted in the input. Removing a lot of code surrounding the tooltip which has now become unnecessary.

Import input now shows error state w/orange border around input and tooltip with static error message.

Initial SB2 Import UI (button in preview modal + import modal that can load projects via url). Preliminary validation on url, still needs error handling.

Update gui to use getter for target costumes

Move active tab state into a reducer