tidy up build files

- remove Gradle wrapper files from nested plugin project
- update .gitignore

Author: adam-enko

.gitignore

@@ -1,9 +1,8 @@
-.idea
+.idea/
 *.iml
-.gradle
-.gradletasknamecache
-build
-out
-target
+.gradle/
+build/
+out/
+target/
+.DS_Store
 local.properties
-node_modules