campaign adjustments - optional helper functions, optional exception handling change

Couple more changes for you...

56a9ce3: changed campaign Sections to a Dictionary<string,string>... I use sections heavily against my templates.

184bfc8: There was an error in the DataMember attribute for BaseTemplateID.  Also added a CampaignCreateTrackingOptions class.

a819b2e: Exception handling: just a humble suggestion... 

509585f: I use these helper functions for creating a MailChimp API compliant date from a .NET date.  IMHO, seems like it might be helpful to support .NET DateTime's throughout your API, but this was a bigger project than I can tackle right now.