Remove panel classes

These classes get put on the containing `atom-panel` element with the new panel API.
Merge pull request #288 from postcasio/patch-2

Remove panel classes
Configurable linter executable timeout

With lint on change disabled, timing out linters doesn't make as much sense.
I implemented this so I could test out how the linter feels with no timeout.

Fixes #204.

Test Plan:
Open a complex Python file for which pylint used to time out. Notice errors
appear after a long time.