Support for go to definition + find type for string module of node requi...

This PR gives the capability to retrieve the module type for require string module by using typeAt hook : 

 * find definition for string module opens the well JS file modules
 * find type (for hover info) displays information of the module.

Here a screenshot when string module "body-parser" is hovered (it call "type" query (findTypeAt)) :

![ternnodetypeat](https://cloud.githubusercontent.com/assets/1932211/5288928/a3f9e168-7b39-11e4-9fe3-5662e3120c61.png)