Message and variable name including '&' destructs toolbox and blocks

[yokobond]

Expected Behavior

'&' should be able to use in message or variable names.

Actual Behavior

When a message or variable contains '&', the message or variable blocks in the Toolbox has no name and blocks in the Code area is empty.

This problem is reported in discussion forum.
When "&" is included in the message, the existing block disappears. - Discuss Scratch

Steps to Reproduce

1. Name a new message or variable with '&'.
2. Open 'Costume' tab and re-open 'Code' tab.

Operating System and Browser

MacOS 10.13.6
Chrome 71.0.3578.98

[apple502j]

Kind of #1077 and regression of #178

[kchadha]

Tracking this in #1077.