Fix 1396, Provide new help page sample override, use it for BSON media type
- https://aspnetwebstack.codeplex.com/workitem/1396
- "Web API Help Pages show garbled samples if BSON formatter is enabled"
- Support HelpPageSampleGenerator with only media type; type no longer needed
- Fallback GetActionSample() lookup to use just media type as a last option
- Provide SetSampleForType() extension which also lacks type parameter
- Initialize ActionSamples to include special case for application/bson

Also use VB short-circuit logical operators where they avoid bugs.  (Not sure
And or Or are worth using except for bitwise operations but I left the rest.)

Current display in application/bson samples is a TextSample containing
"Not displaying binary application/bson content." Suggestions appreciated.

Nit: Reduce duplication between HelpPageSampleKey constructor overloads.