Smooth async support

These changes basically keep source code compatibility for framework users.
If some users have extensions that depend on LocaleFeature, RequestScopeFeature or SkinnySessionFilter, they may need to rewrite them a little bit to accept implicit parameter.

- Add FutureOpsFeature trait for future ops within action methods
- Mixin FutureOpsFeature to SkinnyControllerBase by default
- Add HttpServletRequest implicit param to LocaleFeature, RequestScopeFeature and SkinnySessionFilter methods
- RequestScopeFeature#requestScope[A](String) is deprecated
Merge pull request #162 from skinny-framework/feature/smooth-async

Smooth async support