Core: Fix many "errors"/warnings and coding style (1)

Extractors, worldserver, authserver, shared and collision affected

Errors were found using Cppcheck, open-source static analysis tool

src/server/shared/Cryptography/BigNumber.cpp

@@ -75,7 +75,7 @@ void BigNumber::SetRand(int numbits)
     BN_rand(_bn, numbits, 0, 1);
 }
 
-BigNumber BigNumber::operator=(const BigNumber &bn)
+BigNumber& BigNumber::operator=(const BigNumber &bn)
 {
     if (this == &bn)
         return *this;