Merge several middleware classes

[jeremystretch]

Proposed Changes

Merge the following middleware classes into one:

• APIVersionMiddleware
• DynamicConfigMiddleware
• ExceptionHandlingMiddleware
• LoginRequiredMiddleware
• ObjectChangeMiddleware

Justification

Each of these middleware classes is responsible for a fairly minor yet crucial operation, and it doesn't really make sense that we would need to toggle them individually.

Note that I'm excluding RemoteUserMiddleware from this list, as it holds a considerable amount of custom logic, and we want to ensure it's always processed before the boilerplate stuff.