Added file dialog option for menu items
Fixed type hinting for commands
Implemented upload from computer

This currently fetches assets from the Scratch server. They should actually be loaded from the zip.
Fixed errors with unloaded costumes
Fixed menus always scrolling viewport to top-left
Delayed drawing until insertion into a workspace
Added hidden input type
Fixed loading old mod blocks
Removed error catching in project deserializer
Fixed another error with unloaded costumes
Added Workspace::addAll and Palette::addAll
Switched to addAll
Fixed drawing costume thumbnails larger than the actual costume
Fixed random colors when duplicating or loading blocks
Fixed new sprite buttons in Firefox
Added error handling to local project loading
Fixed file menu items not working when activated with the keyboard

Note: this pops up a warning banner instead of the file dialog in Firefox, requiring the user to allow pop-ups for the website. If this becomes an issue, the menu could instead focus the file input when the item is selected so that it responds to <enter> and <space> and opens the dialog.
Added keyboard shortcut for upload
Added keyboard shortcut for new

This doesn't work in Safari.
Fixed size of sprite thumbnails