Revise alerts code to clarify and reorganize alert type handling

delete existing translations before building translations, to avoid errors

Remove setTimeout for reattaching workspace block listener.

It was causing a bug where switching tabs and adding a sprite would make the workspace blocks not work. Needs investigation.

Send snapshots from the renderer to be saved as project thumbnails

autosave periodically when project is dirty

Disconnect from cloud when entering editor mode on someone else's project

Connect to cloud based on hasCloudData

Queue up messages to send ot the cloud server which accumulate before 
the connection is ready. Add tests for new/updated functionality.

simplified autosave code per rschamp's comments; made isShowingSaveable and autosaveIntervalSecs props

Remove color rotation while saving

Update scratch-paint to the latest version 

Add download and retry saving to saving error alert.

Instead of setting 100% width on the message, causing inappropriate wrapping of the button text. Removed the nbsp in the Try Again text

Track "project changed" state in Redux

I do not like how the alert component is hyper specialized for two distinct use cases. It would be much better to refactor the alerts so that the alerter can just fill the alert with whatever they want. But I do not feel comfortable making that refactor because I know ben and evelyn have gone back and forth about these alerts.

updated scratch-l10n in package.json

We have alerts for this now.
Resolves #3893

Update scratch-vm to the latest version