[VarDumper] Dynamic HTML dumper

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | yes
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #12109
| License       | MIT
| Doc PR        | -

This PR partially reverts #12109 because it didn't take into account that many dumps can share a single style tag.
More importantly, this PR enhance dump rendering with some cute JS navigation effects:
- references highlighting on hovering
- moving references toggling

Here is a screenshot (note the yellow background and the fact that `#2` appears after the first `@2`):
![capture du 2014-10-04 09 45 44](https://cloud.githubusercontent.com/assets/243674/4514936/4431c67e-4b9b-11e4-9809-8d06836be824.png)