Better JavaDocs for Bastion global configuration

[KPull]

The methods exposed by Bastion.globals() need improved documentation in their JavaDocs. In particular, JavaDocs are missing for public methods in Configuration and GlobalRequestAttributes.

We need to explain the following:

• What globals are.
• What the various attributes mean (headers, query parameters, route parameters, etc.). To avoid duplication, we should link to the JavaDocs in HttpRequest.
• What the default values for the globals are.
• That the user should typically clear any globals set, using Bastion.globals().clear(). We should explain this in the method JavaDocs for Bastion.globals().