Suggest changes to two quirky-looking bits

[dougbu]

Update two quirky-looking bits of code

• use SOAP fault when Salesforce handler fails
  • preserve non-200 but successful HTTP status code
• add lots of comments about IsAssignableFrom(...) use in GetDataOrDefault<T>(...)
  • test this method more thoroughly

nits:

• use new C# features
• remove duplicate test data in GenericJsonWebHookReceiverTests
• take VS suggestions, especially in WebHookHandlerContextExtensionsTests

[dougbu]

Rebased on dougbu/infrastructure.updates and changed questions into proposed answers. Bit easier to review with files?w=1 in the URL.

@HenrikFrystykNielsen I would appreciate your thoughts on the SalesforceSoapWebHookReceiver and WebHookHandlerContextExtensions changes. Am I missing something? And, why aren't the unit tests affected? (Should I add more tests?)

[dougbu]

Reopening to see if AppVeyor config is working

[dougbu]

@HenrikFrystykNielsen there's now nothing in this PR except my suggestions (and a few trailing whitespace removals). Please have a look… I am not confident these changes are correct for the existing receivers.

[dougbu]

With thanks for his offline comments, removing @HenrikFrystykNielsen's review request.

[dougbu]

:up::date: and ready for @rynowak

[dougbu]

78491ef819