Rework swarming status page to enable user to see their tasks without being an admin

[GoogleCodeExporter]

Right now only admins can see tasks, it's a poor experience.

This is a tad complex to implement in practice, I see 3 types of use case:
- A user triggered a job for himself. Only the user and admins can see it.
- A bot triggered a job. Anyone can see it.
- Both a user and a bot triggered the same task (e.g. same isolated file and 
same dimension filter), the less restrictive ACL is applied.

So the dashboard listing tasks has to adapt itself to list all tasks visible by 
the user.

Original issue reported on code.google.com by maruel@chromium.org on 14 Feb 2014 at 7:59

[GoogleCodeExporter]

7360937da29e52cae17946dda4c40bd691384ca2 took care of most of the work but not 
everything;
- privileged users can see all tasks.
- normal users can see nothing.

This bug is about normal user to be able to see their own task.

Original comment by maruel@chromium.org on 12 Jun 2014 at 8:57