Record UAA client creation in ServiceDashboardClient

This avoids situations when we might have orphaned clients we created in
UAA, and never been able to reclaim them.

[#62008174]
More validation of dashboard_client on Catalog model

  - Validate that dashboard_client id is unique
  - Also validate that dashboard_client is a hash before validating that
    its fields are correct

[#62008174]
Move towards creating and applying changesets

This will make it simpler to add updates and deletions of UAA clients in
the future.

[#62008174]
Update new relic gem

Signed-off-by: Ruth Byers <rbyers@pivotallabs.com>