Closes #402: tool members resource

[MakotoTheKnight]

This PR is good to go and is eligible for immediate deployment to staging. Notes:

• This adds new resources to the system:

  GET    /v1/tool_members/tool_type/:tool_type/tool_id/:tool_id(.:format)                         
  POST   /v1/tool_members/tool_type/:tool_type/tool_id/:tool_id/request_access(.:format)                               
  DELETE /v1/tool_members/:id(.:format)                                                                                
  POST   /v1/tool_members/tool_type/:tool_type/tool_id/:tool_id/access_request/:id/grant(.:format)                     
  POST   /v1/tool_members/tool_type/:tool_type/tool_id/:tool_id/access_request/:id/deny(.:format)

  These were created to support the new system of adding participants and facilitators to tools.

• Added migrations to the platform to support the new structure of data.