REDIRECT_URL_SUCCESS and REDIRECT_URL_ERROR should not be always mandatory

[plmercereau]

REDIRECT_URL_SUCCESS and REDIRECT_URL_ERROR became mandatory, and HBP won't start without then as per described in var-checks.

However, they will only be used when user registration need to be activated through an activation link (usually sent over an email):

• If auto-activation is enabled, these env vars should not be mandatory
• even when an activation link is used, although it is strongly recommended to define these variables, they should not block HBP to start as in their absence HBP is still able to inform the activation occurred

Generally speaking, documentation is out of sync with the last HBP versions, especially on this one, as this is a breaking change.

[plmercereau]

solved by @elitan