List unsupported browsers (user agents) in Website device

[Whathecode]

Some website studies (introduced in #465) may not be fully supported on certain browsers. E.g., they shouldn't be accessed from a mobile phone browser, or they require advanced browser features which some browsers don't have.

When registering a website device using WebsiteDeviceRegistration, the user-agent HTTP header is passed, which contains information which may be useful to infer whether or not the study is supported on this device.

It could be useful to add support to CARP to parse this information and specify unsupported aspects (e.g., browsers or browser versions) in the Website configuration in study protocols.

However, this needs a bit of thought. What are common scenarios where it is known a study won't be supported?