[AppStream] appstream-glib 0.7.17

[Richard Hughes]

Hi all,

Bugfixes:
 - Add "icon-theme" as recognised component type (Fabio Valentini)
 - Fix building in macOS (Oleksii Samorukov)
 - Fix CI by moving 'future' back a bit (Richard Hughes)
 - Fix Win32 headers (Jehan)
 - Make default content rating values match OARS semantics (Philip Withnall)
 - Properly initialize unique_id_mutex (Marc-Antoine Perennou)
 - Support ${id}/${locale}.qm in addition to ${id}_${locale}.qm (Kalev Lember)

Richard