Fixed bug in authentication service
Fixed bug in authentication service

Set globals to empty object on logout instead of deleting because the
globals.currentUser object is used to check if the user is logged in.

wuyingki/signing2016,cornflourblue/angular-authentication-example,Siddaram-Hebbal/Angular-Authentication,james-portman/angular-authentication-example,lefthook123/angular-authentication-example,james-portman/angular-authentication-example,wzeng/angular-authentication-example,cornflourblue/angular-authentication-example,ivanml/angular-authentication-example,perilainen/hattrick-tippa,perilainen/hattrick-tippa,wzeng/angular-authentication-example,wuyingki/signing2016,Siddaram-Hebbal/Angular-Authentication,perilainen/hattrick-tippa,lefthook123/angular-authentication-example,ivanml/angular-authentication-example