Add possibility to log all lint erros if the user use the shortcut

I find it useful to have the possibility to display all errors and click on the error to go to the correct line/col.

I implement this feature and it works only when you are using the linter shortcut (because I also want to keep the old behavior).

![atomlinter](https://cloud.githubusercontent.com/assets/1850538/3978589/c5444108-2849-11e4-8b64-5508f24c61a6.gif)

I would like to know if you find this feature useful.

If so, I still have some works to do on this PR:
  - Adding specs
  - I don't like the way how I get the line number/col of the error. Need to think about a better solution.

This config lacks context as is. Also, it's confusing how it combines with `showErrorInStatusBar`. E.g. is it valid to have `showErrorInStatusBar` off but `displayAllErrors` on? We should think about how to combine the settings to reduce possible states and also make them easier to understand.

Perhaps something like this makes sense:

statusBar: one of ['off', 'currentLine', 'nearby', 'all']

What do you think?