Implement endpoints for the Unique Devices service.

For comparison and reference, the existing AQS production unit tests can be found in analytics-aqs/test/features/unique-devices/unique-devices.js.

Completion criteria: the following unit tests are implemented:

• should return 200 for expected parameters
• should return 400 when parameters are wrong
• should return 400 when start is before end
• should return 400 when timestamp is invalid
• should return the expected aggregate data after insertion
• should return the same data when using timestamps with hours
• should include offset and underestimate
• should return numeric values as integers
• should parse the device column string into an int