The constructor receives the name of the current mailform provider
together with the pointer to the ResourceBundle where the default
settings are stored.
Title: MailFormProviderList
Description: Represents a handler of a list of known/defined providers of a
mailwebform site, as defined in the application's global properties file.
The constructor receives the Properties object where the providers'
settings are stored, especially the comma-separated list of
defined/active providers which is used to build the internal list of
providers