Refresh views on coverage.json change

In this pull request i will update the coverage views as soon as the coverage.json file changes. I first wanted to use [Node Pathwatcher](https://github.com/atom/node-pathwatcher) but i wasn't able to install it on Windows 8.1 because of node-runas. So i decided to try the unstable `fs.watch` method until that bug is fixed.

- [X] Add a configuration to enable/disable the pathwatcher, because it needs some CPU performance.
- [ ] Initialize fs.watch and refresh on a "changed" event