Adding setLanguage at runtime

[vtikha]

This PR adds the possibility to change the language at run time. for both googleSpeech and googleDialog

The user is now able to modify the language through the following rpc command.

Example of the language switch:

setLanguage en-US

by default, the language and voice codes currently supported are the following, but can be easily extended by adding the required entries in the config.ini

languageCodes     en-US it-IT pt-PT fr-FR en-GB

Here is a list of the possible extra interaction with the module

setLanguage(1:string languageCode);
getLanguageCode();

[lauracavaliere]

All the changes seem correct to me! Thank you @vtikha !

[ilaria-carlini]

Thank you @vtikha! It looks good to me, too.