Add support for reading account credential from an xml configuration file.

[DevAlves1993]

Credential to an account can be in an XML file that can be located in a particular directory or in the same directory as the application's JAR file.

An example of the contents of the credential.xml file :

<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE properties SYSTEM 'http://java.sun.com/dtd/properties.dtd'>
<properties>
  <entry key='username'>akiko</entry>
  <entry key='password'>AIzaSyDKXF9GdXgdboWs3W0hFokBmFF4Fxkyjco</entry>
</properties>

The class that should handle this case will have to implement the basic CredentialAccess interface.

[abdelgeek]

I support the development of this enhancement

[DevAlves1993]

Ok, your contribution will be welcome. So I'll assign you the issue.