Add support for 'lite' schema

[hernandezc1]

The pittgoogle-client currently does not support 'lite' schemas for any survey. A recap of part of a conversation had with @troyraen

• 'lite' schemas should retain the survey’s schema except for the fields that we drop.
• leaning towards adding another dict layer so that the Pub/Sub message payload looks like:

'alert': {...}
'value-added': {our stuff...}