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/core/makeCommand.js

@@ -0,0 +1,25 @@
+const spawn = require('child_process').spawn;
+
+module.exports = function makeCommand(command) {
+  return (cb) => {
+    if (!cb) {
+      throw new Error(`You missed a callback function for the ${command} command`);
+    }
+
+    const args = command.split(' ');
+    const cmd = args.shift();
+
+    const commandProcess = spawn(cmd, args, {
+      stdio: 'inherit',
+      stdin: 'inherit',
+    });
+
+    commandProcess.on('close', function prelink(code) {
+      if (code) {
+        throw new Error(`Error occured during executing "${command}" command`);
+      }
+
+      cb();
+    });
+  };
+};