Convert order status to config entity

Added some more tests.

This patch converts the remaining calls and removes uc_order_status_list().

This patch converts uc_order_state_list() to uc_order_state_options_list() and removes the concept of "order state scopes", which were used to identify "active" order statuses in a non-intuitive way; they were never previously documented. Active orders are now identified by order status weight instead, this is documented in hook_help.

This patch converts UcOrder's order_status property to be an entity reference instead of a string.

There are some followups to this, like removing uc_order_update_status(), converting the uc_state_*_default variables to CMI and possibly converting hook_uc_order_state() to YAML, but I think they are out of scope here and should be dealt with separately. Otherwise I think this is ready to commit? As this is our first real entity conversion for D8 any comments or questions welcome.

Committed #8.

Two further patches attached, to remove uc_order_update_status() and convert uc_state_* to CMI.

10: remove-uc_order_update_status.patch queued for re-testing.

10: uc_order-state-default-cmi.patch queued for re-testing.

10: uc_order-state-default-cmi.patch queued for re-testing.

All patches have been committed, this work is complete.