I forgot that the integration test needs to try clicking, because finding text will find invisible text as well

Questions:
* should the message strings include the number? Or should that get added to the name when the name is defined
* added a new ‘shared-messages’ to handle the definition of backdrop, costume, etc which are used in multiple places, they’re all related to defaults, so should it all be in `lib/default-project`

Provide a from target id when sharing blocks to another target so that variable conflicts can be resolved.

* Export initial states for each reducer
* combine all gui reducers (excludes scratchPaint and intl)
* combine all initial states to create default guiState for preloading in www
* expect all of the gui state to be accessible at `state.scratchGui`

Update calls to addSprite2 to use new API for adding sprites. Cleanup sprite3 representation for uploading a new sprite from an image.

to target pane, which already has all the needed props.

Fixes https://github.com/LLK/scratch-gui/issues/1064