Add http api, user registratiion endpoint, suggestions store

[geoah]

Changelog

• Rename (neo) Store to GraphStore
• Add Suggestion and SuggestionItem models, with gorm tags
• Add Email attribute to User, and add gorm tags
• Add SuggestionStore with SQL persistence using gorm
  • GetAllUsers() ([]*model.User, error)
  • GetUser(name string) (*model.User, error)
  • PutUser(user *model.User) error
  • GetSuggestion(id uint) (*model.Suggestion, error)
  • PutSuggestion(suggestion *model.Suggestion) error
• Add HTTP API
• Add POST /users endpoint for user registration (should find a better path for it)
  • Accepts github_token as query param
  • Gets user's profile from github
  • Gets user's primary and verified email from github
  • Upserts the user's record on the SuggestionStore
• Add mocks and mock generation for stores and queue