Add support for Google Tag Manager

[exlame]

I increased the DB Version but I don't think it is working. I'm doing a fresh installation and it doesn't add the field. Is there another thing to do?

[xcompass]

@exlame sorry for the delay. For the fresh installation, I think you need to add the new field to https://github.com/ubc/iPeer/blob/master/app/config/sql/ipeer.sql and https://github.com/ubc/iPeer/blob/master/app/config/sql/ipeer_samples_data.sql