fix(settings): show "change password" only for local account

fix(settings): show « change password » only for local account and hide
for account signed up over social network

- add new method `isPasswordChangeable` in Auth.service.js;
- modify settings view to show « change password » only for local
created account;

Closes #343
fix(auth.svc.coffee): fix isPasswordChangeable

fix error in isPasswordChangeable method of auth.service.coffee