2020-05-22 Most of DIY Flow, Datadog metrics, Partner/State refactoring

• Start your fsa #172730228 (#267)
• add datadog metrics api module and instrument first metric
• [#172729953] Add DIY Email page
• Moves check email page into diy flow after email address form page
• Adds email address form page for diy intake flow
• Remove partner routing constants from EitcZendeskInstance
• Adjust checkmark list style
• [#172728386] Add DIY Personal Info page
• [#172928066] Ensure that the spec for "re-assigning" a partner after
  personal info sets up the test with prior assignment & no ticket ID
• [#172942889] Fix partner logo paths
• Handle missing state values on intakes
• Adds partner source codes and states
• replaces homepage dollar hero with new illustration
• add GA on successfully submitted page so we can track conversions
• [#172730910] Add "returning client" page
• removes idme artifacts
• Add diy signpost page
• adds diy/check-email page, for #17273000
• copy change on stimulus-recommendation
• Add source routing for United Way California: Koreatown
• changes title copy on tax questions page