Core/Config: User-friendlyfy configuration parsing errors

It will now print useful error messages that pinpoint the issue
with the config file (missing file, bad syntax, etc)

In memory of MitchesD that lost 18 hours finding a problem with
his config because of a duplicated line.

src/server/worldserver/Main.cpp

@@ -109,10 +109,10 @@ extern int main(int argc, char** argv)
         WinServiceRun();
 #endif
 
-    if (!sConfigMgr->LoadInitial(configFile))
+    std::string configError;
+    if (!sConfigMgr->LoadInitial(configFile, configError))
     {
-        printf("Invalid or missing configuration file : %s\n", configFile.c_str());
-        printf("Verify that the file exists and has \'[worldserver]' written in the top of the file!\n");
+        printf("Error in config file: %s\n", configError.c_str());
         return 1;
     }