admin error message for non-admins

[stevenolen]

Currently, the frontend shows a blank page and throws an exception when a non-admin attempts to view an admin-only page. Maybe a simple "you do not have access to this content" message can be displayed in this case?

to replicate: visit test.ohmage.org/web/#admin as a non-admin

Fri Apr 12 09:51:14 GMT-700 2013 edu.ucla.cens.mobilize.client.MainApp
FINE: History Token Fired = 'admin' 20A8226802F6D5F8661926E8BF10F62C.cache.html:4916
Fri Apr 12 09:51:14 GMT-700 2013 com.google.gwt.logging.client.LogConfiguration
SEVERE: One or more exceptions caught, see full set in UmbrellaException#getCauses
com.google.gwt.event.shared.UmbrellaException: One or more exceptions caught, see full set in UmbrellaException#getCauses
    at Unknown.dl(Unknown Source)
    at Unknown.Qu(Unknown Source)
    at Unknown.Su(Unknown Source)
    at Unknown.hu(Unknown Source)
    at Unknown.Nab(Unknown Source)
    at Unknown.Xt(Unknown Source)
    at Unknown.Pab(Unknown Source)
    at Unknown.anonymous(Unknown Source)
Caused by: com.google.gwt.core.client.JavaScriptException: (TypeError): Cannot read property 'fb' of null
    at Unknown.hbb(Unknown Source)
    at Unknown.nbb(Unknown Source)
    at Unknown.Wob(Unknown Source)
    at Unknown.Kob(Unknown Source)
    at Unknown.SAb(Unknown Source)
    at Unknown.$7(Unknown Source)
    at Unknown.Wt(Unknown Source)
    at Unknown.su(Unknown Source)
    at Unknown.hu(Unknown Source)
    at Unknown.Nab(Unknown Source)