SessionFlash test -- more robust code in lib/session.
Moved the default context (DevContext which handles request parameters) from
lib/web to app/filters as params.go

Refactored context chaining to remove doubly linked list [as we use simple iteration anyways]
as well as passing the chain list into TestContext.

This way you can test that the context-chain you belong to supports features you need to
service a request.

This allows, for e.g, the FlashContext to piggyback on the SessionContext for session storage.
Refactored controllers to support new ContextChain setup.
(They are no longer passed a parameter context by default; instead it is now part
of the default chain builder.)
Routes updated so that they compile & pass additional runtime safety checks.
Merge branch 'develop/refactor-context'