[wip] Add Versions List, Version API (v2) resource

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Use simple require for spec helper
Add specs for API v2 version index
Add specs for API v2 version show
Extract methods used for multiple project selection
Implement version index with multiple projects
Test handling of shared versions
Query projects shared versions
Test projects references in shared versions
Aggregate projects for shared versions
Remove show endpoint
Test version ids filter
Implement version ids filter
Test API v2 version index response
Implement API v2 version index response
Remove superfluous let statement
Use simple require for spec helper
Merge pull request #1859 from opf/feature/15077-api-v2-version-resource

15077 api v2 version resource