site: ios: Update links to M3 tarball, once it is there

Once the M3 bits (iOS lib + TODO DEMO APP) have been release (lib on cocoapods + M3 tarball on gh; app only tarball)

We need to update the tarball links on the following pages:
The homepage:
http://aerogear.org/index.html

The download page:
http://aerogear.org/download/