Refactor Snap! edits into changesets

[cyderize]

Refactor Snap! edits into changesets as per #370. It may be wise to merge this into its own branch rather than master in case there are unforeseen bugs caused by this.

Not all changes could be moved to the changeset files, but each function which might cause a merge conflict is now marked with a comment so that the changes can be kept track of.

• Refactors blocks.js to be identical to upstream Snap! file.
• Refactors byob.js to be identical to upstream Snap! file.
• Refactors some of the changes in gui.js into changesToGui.js. Areas that still differ have been marked with comments.
• Refactors threads.js to be identical to upstream Snap! file.
• Refactors some of the changes in objects.js into changesToObjects.js. Areas that still differ have been marked with comments.
• Refactors some of the changes in store.js into changesToStore.js. Areas that still differ have been marked with comments.

Closes #370.

[stevenbird]

Thanks @cyderize – checking this out...