Use random salt for each fingerprint key

Salt length depended on fingerprint name length, which lead to weak salts in some cases
It's now a fixed length (12 bytes)

Akari.Prototype.Server/Services/FingerprintManager.cs

@@ -67,6 +67,8 @@ namespace Akari.Prototype.Server.Services
             {
                 SaveFingerprints();
 
+                _authManager.GenerateSalt(name);
+
                 return true;
             }