Update Sign-in text when in the Scratch Editor

[techwonder21]

Expected Behavior

Sign-in text should be the same across both the Project Page and Scratch Editor

Actual Behavior

Sign-in text on the Scratch Editor is different than the Project Page

Steps to Reproduce

1. Visit a Scratch project in 3.0
2. Change "project" to "preview"
   https://scratch.mit.edu/preview/237965780/editor/
3. Click the "Sign in" button while in the Scratch Editor and notice the text "general.username, general.password, general.signIn, login.needHelp"
4. Click the "See Community" button, then click the "Sign in" button and notice the correct sign-in text.

Operating System and Browser

Chrome 70, macOS High Sierra

[techwonder21]

@ChampikaF @rschamp @thisandagain

[thisandagain]

@benjiwheeler @chrisgarrity I'm fairly certain this is already being tracked, but couldn't find it. Can you please prioritize?

[benjiwheeler]

#3601 exists; this should have been solved by #3602