Also make 403s to get server details more obvious rather than a silent failure.

The following revision refers to this bug:
  https://chromium.googlesource.com/external/github.com/luci/luci-py.git/+/feb72d34696812e45df91585a1bd28162e0b7b64

commit feb72d34696812e45df91585a1bd28162e0b7b64
Author: kjlubick <kjlubick@google.com>
Date: Thu Nov 17 20:06:02 2016

Move error-toast up and Give a warning if clientid is not set

This makes sure all pages have an error-toast element. This allows
server details problems (typically 403) easier to see and address,
especially when setting up a new instance.

The pages now will be bright red and easily visible if client id
is not set.  Again, this is useful for setting up a new instance.

BUG= 665442 

Review-Url: https://codereview.chromium.org/2511463003

[modify] https://crrev.com/feb72d34696812e45df91585a1bd28162e0b7b64/appengine/swarming/ui/build/elements.html
[modify] https://crrev.com/feb72d34696812e45df91585a1bd28162e0b7b64/appengine/swarming/ui/res/imp/botlist/bot-list.html
[modify] https://crrev.com/feb72d34696812e45df91585a1bd28162e0b7b64/appengine/swarming/ui/res/imp/botpage/bot-page.html
[modify] https://crrev.com/feb72d34696812e45df91585a1bd28162e0b7b64/appengine/swarming/ui/res/imp/common/swarming-app.html
[modify] https://crrev.com/feb72d34696812e45df91585a1bd28162e0b7b64/appengine/swarming/ui/res/imp/index/swarming-index-demo.html
[modify] https://crrev.com/feb72d34696812e45df91585a1bd28162e0b7b64/appengine/swarming/ui/res/imp/tasklist/task-list.html
[modify] https://crrev.com/feb72d34696812e45df91585a1bd28162e0b7b64/appengine/swarming/ui/res/imp/taskpage/task-page.html

This is live on chromium-swarm (although since it's set up properly, you can't see it)