Fix icons for lines that use maki (fixes #1371)

Generate a single feature-icons.json and feature-icons.css.
In the JSON, features with a line icon are indicated by the
presence of a `line` property. PresetIcon looks for this to
determine whether or not to add the `preset-icon-line` class.
New line icons may be added by editing line-icons.json.

data/data_dev.js

@@ -14,7 +14,7 @@ iD.data = {
             path + 'data/presets/categories.json',
             path + 'data/presets/fields.json',
             path + 'data/imperial.json',
-            path + 'data/maki-sprite.json',
+            path + 'data/feature-icons.json',
             path + 'data/operations-sprite.json',
             path + 'data/locales.json',
             path + 'dist/locales/en.json'
@@ -32,7 +32,7 @@ iD.data = {
                     fields: data[7]
                 },
                 imperial: data[8],
-                maki: data[9],
+                featureIcons: data[9],
                 operations: data[10],
                 locales: data[11],
                 en: data[12]