fix(schema): allow extract to accept omit/remove flags

Closes #371.

Author: bebraw

schema/valid.json

@@ -1,6 +1,8 @@
 {
   "allChunks": { "type": "boolean"},
   "disable": { "type": "boolean" },
+  "omit": { "type": "boolean" },
+  "remove": { "type": "boolean" },
   "fallbackLoader": { "type": "string" },
   "filename": { "type": "string" },
   "loader": { "type": "string" },