[managed] Added feature header to gauge usage of table types
[managed] Added feature header support for custom API overloads
[managed] Addressed code review feedback for telemetry feature.
[managed] Added telemetry for MobileServiceCollection
[managed] CR feedback
[managed] Features CR feedback:

- FeatureCodeAttribute made into a general-purpose class
- Factor features string code out of HTTP client into helper class
[managed] Cleanup for features (telemtetry) code
Merge pull request #329 from carlosfigueira/dev

[managed] Add telemetry information for features used in the client SDK