Password reset (#448)

* Password reset

* Various improvements and fixes for password reset

- Reorganize src/mail.rs to make it  cleaner
- add a build_mail function
- only make the requests invalid after 2 hours
- avoid infintely-growing list of requests by deleting them once completed, or after 24 hours
- avoid sending many requests for the same user
- validate the password reset form

* Avoid locking so many times

Fix durations

* Remove old requests even if the current one is not valid

* Remove unused feature

* Also remove the custom_derive and plugin features while we are at it

* Forgot a 0 è_é

* Avoid panicking while owning a request lock

* Use master branch of lettre so that we can build with the latest OpenSSL

* Fix the debug mailer

templates/session/login.rs.html

@@ -16,4 +16,5 @@
         @input!(ctx.1, password (password), "Password", form, errors, "minlenght=\"1\"")
         <input type="submit" value="@i18n!(ctx.1, "Login")" />
     </form>
+    <a href="@uri!(session::password_reset_request_form)">Forgot your password?</a>
 })