Localhost system access settings

Add settings for localhost system requests:

usergrid.sysadmin.localhost.only:
true = allow sysadmin requests only via localhost
false = non-localhost requests can provide sysadmin credentials (default)

All sysadmin requests still require credentials.
usergrid.sysadmin.localhost.requires.credentials:
true = localhost sysadmin requests require credentials (default)
false = localhost sysadmin requests do not require credentials