Restore symlinks in FacebookSDK.Framework before build

[vladimir-kotikov]

This PR adds hooks for save/restore symlinks metadata. This fixes issue when iOS custom frameworks is being broken when plugin installed from CPR/NPM. See https://issues.apache.org/jira/browse/CB-6092 for details

Save is being performed each time, plugin is being packaged or published through NPM. Restore - each time when iOS project is being compiled.

Quirks:

1. Since cordova doesn't respect existing package.json while publishing plugin to CPR and thus doesn't exec prepublish script, the generated symlinks metadata already included in this PR. It could be also generated manually by running npm run prepublish inside of plugin directory.
2. before_compile hook is available in cordova@>=4.0.0 only so the symlinks won't be restored in earlier versions of cordova.

[jfaris]

Thanks @vladimir-kotikov for taking the time to fix this properly. This is much better than just copying the files and creating a huge tarball.

Unfortunately I don't think it will work for PhoneGap Build because they don't support hooks (phonegap/build#425) and phonegap is still at version 3.7 so won't have the before_compile hook. These are problems with PGB, not this PR.

Regarding Quirk 1 above: we could just maintain the metadata json file manually rather than running the script. The resulting JSON is so simple and the script isn't run automatically anyway. It would cut the size of this pull request in half. What do you think?

[vladimir-kotikov]

Well, once Cordova plugin registry became read-only, the only way to publish plugin will be an NPM, so the prepackage hook still could be useful 😄

[aogilvie]

NICE. Thanks Microsoft too.