Validate collaborators invited twice

[ismaelbej]

Changes

• Back:
  • Return error message when trying to add an existing collaborator to a project
• Front:
  • Remove unused function loadCollaboratorToEdit from CollaboratorIndex and properties confirmationText, onConfirm from InviteModel
  • Modify changeEmail action and reducer to accept a list of collaborators to validate the email isn't included between the collaborators
  • Show error message resulting from the email validation

Closed #1786

[ismaelbej]

@matiasgarciaisaia It should be ready for another review. Friday commit was missing using the collaborators from the redux storage, instead of using properties. If found that other actions use getState() to read the redux storage.