[vkmk] Communicate order totals to member system

[wvengen]

When Foodsoft takes over dry ordering functionality, it needs to communicate the order totals to the members system (instead of the dry system, which currently happens).

Depends on https://www.assembla.com/spaces/vokomokum/tickets/251

• [x] Allow to send totals to members system using its charge-members endpoint
• [x] Do this when settling an order (instead of creating financial transactions in Foodsoft)
• [x] Store authentication cookies in user object so they can be used in the Order model
• [x] Redirect Foodsoft's Payments url to members system
• [x] Show message returned by the charge-members endpoint in Foodsoft
• [ ] Make sure error handling works (incl. member to be charged for isn't present in vkmk-members)

[wvengen]

What remains is testing, when the memberstest system is back again.

[wvengen]

Mostly implemented on branch acceptance/vokomokum-dry.

[wvengen]

This has moved to https://github.com/vokomokum/foodsoft, see also https://github.com/vokomokum/vkmkm-deploy/issues/1.