Autogenerate spec version for modpacks

[HebaruSan]

Motivation

#2971 updated the spec version for modpacks from v1.6 to v1.18 so the license could validly be set to Unlicense. In principle, anytime we add a new license or change anything else that might depend on the spec version, we need to bump the generated modpacks' spec version by hand. And in fact we've already missed this once, when the MPL-2.0 license was added in v1.30.

Now that we have a way to calculate spec versions automatically (see #4155), it makes sense to eliminate this as a manually maintained item.

Changes

• SpecVersionTransformer.MinimumSpecVersion is moved to a new static class SpecVersionAnalyzer in Core
• A new override of MinimumSpecVersion accepts a CkanModule parameter instead of JObject (converted with JObject.FromObject)
• RegistryManager.GenerateModpack uses SpecVersionAnalyzer.MinimumSpecVersion to set the default spec version before it returns its module
• EditModpack.ExportModpackButton_click uses SpecVersionAnalyzer.MinimumSpecVersion to set the spec version after the user finishes editing and before the modpack is saved to disk