Add BatchMetricsQueryHandler and tests

Add RollupTestUtils
Refactor plot request parsing logic into its own class
Change MetricData to also contain 'type' of metrics
Changes to serializers for JSON output
Add HTTP endpoint & handler for batched metrics
Use enum for MetricData types
Send out max limit as part of response error message
Change type from 'numeric' to 'number'
Merge pull request #143 from lakshmi-kannan/bf_add_multi_fetch_support

Add batch metrics fetch support