US2626 changes based on feedback
- Add application name in Usage and UsageRecord models
- Change 'price' to 'usage_rate_usd' in rest cartridge model
- Change 'charges' to 'usage_rates' in rails configuration
- Rails configuration stores usage_rates for different currencies (currently only have usd)

Pass app name to track_usage

Add app_name to usage model unit tests
Merge pull request #1267 from pravisankar/dev/ravi/us2626-feedback

Merged by openshift-bot