Reworked linter and reporter so that there can be one per editor so that...

... in split view, things continue to work when switching between the views

https://github.com/MiguelCastillo/Brackets-InteractiveLinter/issues/55
I've long thought of moving this inline - all we do here is check if the gutterId is "interactive-linter-gutter", and call a function with the line index. What do you think?