Add custom parameters to $count and ODataTypeCast paths' Get operations

[irvinesunday]

Fixes #207

This PR:

• Adds custom parameters to $count and ODataTypeCast paths' Get operations where either the target navigation property or navigation source has been appropriately annotated with the CustomHeaders property in its ReadRestrictions annotation.
• Adds a new test class and test methods for DollarCountGetOperationHandler.cs --> DollarCountGetOperationHandlerTests.cs
• Updates some tests
• Updates some integration test files

NB: In response to this comment, we already do add custom headers to navigation properties, and index endpoints where appropriate.