This change solves the User's API problem when you want to create an user that its email hasn't been verified yet but it exist.
At now, you can resend invitation email using endpoint /users/{id}/resend-invitation
Fixes#184
Move client authentication into its own middleware and provide
differentiation between HTTP requests that do not provide
credentials (401) and requests that authenticate as a non-admin
user (403).
Closes#152
This commit moves the user.Manage to its own package (user/manager)
so it can import the connector package in a later commit.
For clarity, it renames "Manager" to "UserManager" using gorname.
This commit has no functional changes.
Invite emails are essentially just reset password emails with a
different template (though this can and probably will change (slightly)
in the near future)
