Merge pull request #326 from hasankhan/dev

[client][managed][test] updated e2e test app and service to reference latest nuget packages
[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
[iOS] Update const usage

Fix issue with const clash with the messaging framework
[iOS] Add change log for 1.2.3 release
[iOS] Increment release to 1.2.3
Merge pull request #332 from phvannor/dev

[iOS] Update const usage
[client][managed] Throw a conflict exception on 409