Added initial composer.json. WIP

@sandeepone Please add `cms` package  to `gleez` account: https://packagist.org/ and at the same time, check fields please. For fields available in composer.json see http://getcomposer.org/doc/04-schema.md

`@todo`:
+ Add Mango Reader
+ Add Cerber Theme
+ Add `suggest` field
+ Add `version` field