[FastCgi] Prepare ConfigurationManager for cleanup

Starting by removing the (unused) possibility of having duplicate keys.
[FastCGI] Remove unused Hash from ConfigurationManager
[FastCgi] Switch to Dictionary as config backend

Switched from NameValueCollection to Dictionary in
ConfigurationManager.cs. Added DictionaryExtensions.cs.
[FastCGI] Avoid creating unused temp variables, fix small error in default for uint16
[FastCgi] Formatting fix
Merge pull request #14 from miniBill/configmanager_dictionary

ConfigurationManager: dictionary backend