Add contains operator to ContentType objects

[osipxd]

Subsystem
Core

Motivation
Add a simple way to check if a content type has one of the well-known types. This check should be case-insensitive, that is why it is error-prone to check content type using contentType.startsWith(...)

Solution
Add an operator contains to ContentType objects checking that the content type prefix is equal to the expected type name ignoring its casing.

This is a draft PR to validate the idea.

[bjhham]

I dig it 😎