Revise multi market mode

[erikhofer]

Multi market mode as it is now seems a bit too complex for its benefits. Currently the server allows the following modes:

• DISABLED -> there are no markets
• PATH -> market slug is part of the path (e.g. exmaple.com/de/products/5)
• SUBDOMAIN -> market slug is a subdomain (e.g. de.example.com/products/5) (not implemented yet)

There are also "market agnostic" paths like /csrf-token.

The actual plan for the first community is the following:

• server at api.example.com with mmm=PATH
• client at example.com with mmm=PATH

Concerns:

• It's probably not a common use case to use SUBDOMAIN on the server; it may be usefull to point different subdomains to differnet IPs (by server location) but they'd have to access the same database anyways (atm).
• On the client SUBDOMAIN isn't really viable because then you can't switch to a different market without page reload
• If mmm is enabled but there is only one market, this is kind of the same as DISABLED
• What if mmm is enabled but there are no markets (yet)?

Proposal: Drop support for different market modes. Make PATH the only option. Have a default market; there must be at least one market

Cons:

• If there is only one market, it still has to have a slug. This is, at least on the client, not ideal.
  • If the user only ever sees URLs with the slug included, the default one could be a fake one like app
  • Default one could be really short and non-disturbing like m

[erikhofer]

Proposal approved. Implementation: #30