Move coffeelint settings to external file

The motivation is for this is to allow `coffeelint` config to be shared by
`script/grunt coffeelint`, global `coffeelint` and inline linting via
`AtomLinter`.

Test Plan:

Made some deliberate lint errors then ran `script/grunt coffeelint` and
verified the output looked the same with and without this change.

build/Gruntfile.coffee

@@ -144,12 +144,7 @@ module.exports = (grunt) ->
 
     coffeelint:
       options:
-        no_empty_param_list:
-          level: 'error'
-        max_line_length:
-          level: 'ignore'
-        indentation:
-          level: 'ignore'
+        configFile: 'coffeelint.json'
       src: [
         'dot-atom/**/*.coffee'
         'exports/**/*.coffee'

coffeelint.json

@@ -0,0 +1,11 @@
+{
+  "indentation": {
+    "level": "ignore"
+  },
+  "max_line_length": {
+    "level": "ignore"
+  },
+  "no_empty_param_list": {
+    "level": "error"
+  }
+}