Webhook Validation Fix

Update Payments API support

Bump version

Update sample project dependencies

Add support for setting webhook ID in config

- If set, calling WebhookEvent.ValidateReceivedEvent() will use this webhook ID when performing the validation.

Update CHANGELOG.md

Update sample dependencies

Add open source strong-name key

- Addresses #101
- SDK and Tests projects are now both setup to be signed with a strong-name key in the projects here on GitHub.
- NOTE: The released version of the SDK will continue to be signed with a private strong-name key.

Update CHANGELOG.md

Update appveyor.yml

- Remove building Debug configuration from public CI builds.