Added .reviewboardrc file
Move Calendar extension into xface-extension-calendar repo

1. Added plugin.xml
2. Added js code for Calendar extension
3. Added Calendar extension souce code for ios platform
Add 'xface-extension-calendar/' from commit '8f1e51da55391c8ea3bf424b3b6b3963c07cea2e'

git-subtree-dir: xface-extension-calendar
git-subtree-mainline: e4e60bd48edb62c938d11480cc849676bf7d51f9
git-subtree-split: 8f1e51da55391c8ea3bf424b3b6b3963c07cea2e