[PoC][WIP][Profiler] Add ability to store request duration time

In overall: I know that current code is BC break, and it's not working as expected (yet =)), it's more like RFC, that such functionality could be useful in Symfony Profiler or not.

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| BC breaks?    | yes [1]
| Deprecations? | no
| Tests pass?   | no [2]
| License       | MIT

[1] This will be fixed after getting some feedback (not sure yet which way =))
[2] This will be fixed in next few days, only file based fail now

View PoC:
![form](https://cloud.githubusercontent.com/assets/67402/2649073/9f971952-bf5e-11e3-9b29-762cb9c1f93a.png)
![list](https://cloud.githubusercontent.com/assets/67402/2649074/9f9bff8a-bf5e-11e3-8726-f3116940f34f.png)