Unique clients metric is incorrect

## Expected Behavior
When sending metrics such as security checks, the unique client count should only increase by 1 irrespective of how many times those metrics are sent from that client.

## Actual Behavior
Each time a metric is published the unique client count increased by 1. This does not currently happen with app and device metrics - only with custom metrics such as security.

## Steps to Reproduce the Problem
The easiest way to reproduce this is using one of the showcase applications. Using the cordova application and the mobile core with metrics running:
1. Run the device and navigate to the authentication page. The unique client count in displayed in Grafana should increment by 1. If the app is rebuilt and rerun and the authentication page loaded again, the count stays at 1.
1. Navigate to the Device Trust page. This sends four metrics in a security array, as defined by this api. The count here will only increase by 1.
1. Re-load the page and the metrics will be re-sent. The unique client count will now increase by 1.

## Specifications

- Metrics API version: 0.0.12