webadmin: Change query context from String to Object

There's no reason to limit the context of a query to be represented by
a String. Also, changed the argument's name from "context" to "state",
to comply with the more widely-used argument related to action
running.

Change-Id: Ib5a0e51fdf3eeb092d41a4724be89f432d975a83
Signed-off-by: Lior Vernia <lvernia@redhat.com>