Further RNPM integration

Summary:
This commit removes `rnpm` folder that we left during initial merge to keep the diff cleaner. The `core`, `link` and `install` have now the same directory structure as any other command to make development more natural for all of us.

From most notable differences:
1) the `src` folder is now gone. The new structure should make it easier for people to work with the stuff and also move us closer to 100% rnpm integration,
2) There's also no `package.json` present in any of the `rnpm` packages, since they are no longer standalone modules,
3) There's no `bugs.url` in link.js since main package.json of React doesn't specify it. Decided to hardcode it to facebook/react-native since it's really unlikely to change. If one would prefer to use pkg.bugs.url as before, a separate PR modifying package.json should be sent.
Closes https://github.com/facebook/react-native/pull/9509

Differential Revision: D3751115

fbshipit-source-id: 74ae8330f7634df0887ad676808f47eee4b8de85

local-cli/link/ios/addFileToProject.js

@@ -0,0 +1,14 @@
+const PbxFile = require('xcode/lib/pbxFile');
+
+/**
+ * Given xcodeproj and filePath, it creates new file
+ * from path provided, adds it to the project
+ * and returns newly created instance of a file
+ */
+module.exports = function addFileToProject(project, filePath) {
+  const file = new PbxFile(filePath);
+  file.uuid = project.generateUuid();
+  file.fileRef = project.generateUuid();
+  project.addToPbxFileReferenceSection(file);
+  return file;
+};