Plugin config, enable/disable, customization

Hi!
I've added some functionality to your plugin and thought that maybe you'd like to merge it. I think these are all useful simple features that people expect from a plugin.

So, this patch includes three main features:
  * A plugin-level "standard" *.sublime-settings config file instead of `local_settings.py`
  * A menu option that enables/disables checking for a specific view, and that can be bound to a key combination
  * Status bar display of plugin state (enable/disabled)
  * Two new configuration options:
     - `enabled_by_default`, that allows people working on heavy projects to leave the plugin off by default
     - `highlight_color`, which allows the user to set the theme style that will be used for highlighting

I think that's it. I hope it's not too many changes for a single pull request.

Thanks for the good work!