Bug 20581: API provide status_alias embed

Bug 20581: API provide status_alias embed

- This patch provides the illrequests API route with an additional embed,
called 'status_alias'. Requesting this embed returns an object for the
request's status_alias authorised value, or null if one is not set.
- This patch also adds the new status_alias as a default embed on the API
call made by the illlist view

Signed-off-by: Niamh.Walker-Headon@it-tallaght.ie
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>