Resolve compatibility conflicts after multi-host merge

[HebaruSan]

Problems

• Multi-hosted mods on both GitHub and SpaceDock can have inflation errors saying
  ksp_version mixed with ksp_version_(min|max). GitHub download fallbacks for applicable mods KSP2-NetKAN#125 had to use overrides to get around this:

  x_netkan_override:
    - version: 1.2.3
      override:
        ksp_version_max: 0.1.2

• Between GitHub download fallbacks for applicable mods KSP2-NetKAN#125 and Multi-download for Inputbinder KSP2-NetKAN#127, Inputbinder had a download property containing an array with one element. This is odd and unnecessary.

Cause

• SpaceDock adds a ksp_version / ksp_version_max based on the game version the uploader selects that isn't available on GitHub, so the GitHub branch of the netkan inflates with just ksp_version_min, while the SpaceDock branch has ksp_version, and the two branches are merged just by combining their JSON properties, which creates inconsistent metadata with both ksp_version and ksp_version_min set.
• NetKAN.Model.Metadata.MergeJson was generating an array regardless of how many download URLs it had. Single-host netkans weren't affected because that function is only called for multi-host.

Changes

• Now after we merge the properties, NetKAN.Services.ModuleService.ApplyVersions (which is the logic we use elsewhere to combine compatibility from different sources) is used to reconcile these properties. This should make SpaceDock's compatibility carry through to the merged netkan without the need for overrides.
• Now if a merged module only has one download URL, the download property will be a string rather than an array

I'll remove the overrides from KSP-CKAN/KSP2-NetKAN#125 in a subsequent pull request.