Add a LOGIN_IN_TOOLBAR constant to decide whether to show the login/logout link in the toolbar

It'd be nice to be able to have the login button/username in the toolbar independant of the fact that the header is shown or not. Adding a new configure option defaulting to false does the job here, i can have my own header without the login goo, which is moved to the toolbar depending on LOGIN_IN_TOOLBAR.

Of course GEOR_custom.js in template profile should be updated with that new option.