Add warning if WAGTAILADMIN_BASE_URL is undefined
Add warning if WAGTAILADMIN_BASE_URL is undefined

zerolab/wagtail,rsalmaso/wagtail,rsalmaso/wagtail,wagtail/wagtail,wagtail/wagtail,wagtail/wagtail,zerolab/wagtail,zerolab/wagtail,rsalmaso/wagtail,thenewguy/wagtail,thenewguy/wagtail,thenewguy/wagtail,wagtail/wagtail,zerolab/wagtail,rsalmaso/wagtail,wagtail/wagtail,thenewguy/wagtail,thenewguy/wagtail,zerolab/wagtail,rsalmaso/wagtail