Fixes #7423: Allow Bastion to be used by other UI plugins.

Good question. If you look inside the Rakefile, you will see that for plugins I point grunt at the Gruntfile copied down to `.tmp/bastion` so that all of those Grunt tasks can be re-used and configured the same way for plugins. However, I need to tell Grunt to use the current directory of the plugin to get the pathing of assets correct. This means we either move the .jshintrc into the task config or we copy .jshintrc into the plugins folder.