Skip over form steps that provide a single choice only (or none)

[hholzgra]

It is possible to configure a MapOSMatic instance with only one base layer stylesheet, no overlays and -- in the future -- only a single layout and fixed paper format.

This may make sense for instances that server a rather specific purpose / use case only.

In such cases form steps that only allow for a single choice anyway should not even be presented to the user, so streamlining the form entry process as much as possible