Parameterise query for load_problem_or_display_error

By default `load_problem_or_display_error` only allows reports
that are owned by the current cobrand to be displayed.
Allowing the base query to be passed in as a $problems parameter
means that the function can be reused in places where the base
set of problems isn't limited to those owned by the current cobrand.
Give problem confirmation page its own URL

Previously report confirmation page was only shown in
particular circumstances (generally if the user wasn't logged in)
and at a single-use URL (the token link from the confirmation email).
It will be advantageous to show the confirm page at other points so
this commit exposes a new URL /report/confirm/<id> that shows a
report's confirmation message.
Show confirmation page for non-cobrand-owned reports

If a logged in user submits a report that is sent to a council
other than the current cobrand's, display the confirmation message
so that they understand where their report has been sent and why
they're being redirected to the main FMS site.