Show all recommendations of metapackages in GUI

[HebaruSan]

Problem

If you use the "Install from .ckan..." menu option in GUI, as of #2577 some modules may be missing.

Cause

CanInstall decides whether a list of modules can be installed by creating a RelationshipResolver and checking whether its mod list has at least as many elements as it's trying to install:

CKAN/GUI/MainRecommendations.cs

Line 152 in 1bbd2fd

if (resolver.ModList().Count() >= toInstall.Count)

The list on the right includes the .ckan file itself, which has IsMetapackage = true.

Unfortunately RelationshipResolver excludes metapackages from ModList(), so such modules would not be included on the left:

CKAN/Core/Relationships/RelationshipResolver.cs

Lines 490 to 493 in 1bbd2fd

	private void Add(CkanModule module, SelectionReason reason)
	{
	if (module.IsMetapackage)
	return;

So CanInstall's check will fail when installing a metapackage, unless it has a bunch of extra dependencies.

Changes

Now we exclude metapackages from the right side of that comparison, and all recommendations from the .ckan file are shown in GUI.

Fixes #2652.