[CR-424660] Rename `Register` link to `Sign Up` in toolbar
[CR-424660] Rename `Register` link to `Sign Up` in toolbar

cjlee112/socraticqs2,raccoongang/socraticqs2,cjlee112/socraticqs2,cjlee112/socraticqs2,raccoongang/socraticqs2,raccoongang/socraticqs2,cjlee112/socraticqs2,raccoongang/socraticqs2