Move update methods and add statusbar

In this pull request i will move the update methods to the `coverage.coffee` file to update the StatusBar and CoveragePanel at once without parsing the coverage data twice.

I will also add a icon to the statusbar, with which it will be possible to toggle the coverage panel. It will also be tinted in the color of the current coverage status (red, orange, green).

- [X] Move update methods from coverage-view.coffee to coverage.coffee
- [X] Rename coverage-view to coverage-panel-view
- [x] Add statusbar view
  - [x] Assign the [octoicons pulse icon](https://octicons.github.com/icon/pulse/)
  - [x] Toggle coverage panel by clicking on the statusbar icon
  - [x] Tint the statusbar icon in the color of the current coverage