Rethink some of the wording and names

[felipesere]

There are some funky names that could be tightened up:

• [x] The entire notion Advisor.Core and non-Core things can be flattened
• [x] QuestionnaireProposal, for when we create a new Questionnaire
• [x] Questionnaire.Form, for when we present data. It's not even an actual struct.
• [x] The AdviceRequest module should go in favor of a more connected DB model (that name could be reused?)
• [x] Reconsider singular/plural version of Person/People, Question/Questions,...