Updates for RC 1.0.x, Kolab style sheet compatibility, and other features

The basic thrust of my update is to build upon Sebastian's work to bring the plugin up to Roundcube 1.0.x compatibility and beautify the plugin.  I've also added a slight change to make this compatible with the changes Kolab has made to the base style sheet.  Given the databases are configured correctly and the config file is properly updated, this plugin should now work with standard or Kolab installations without modification.

It brings with it some additional features by Sebastian (that honestly, I haven't looked at), and some improved documentation in the README.md file, a new amacube.mysql.schema file briefly describing a new database the plugin seems to need, adding a CHANGELOG file, and a composer.json file describing the plugin.  The README.md section for TODO has been updated to reflect functionality I plan to add.

The versioning is derived by using Sebastian's update as 0.2.0, and my update as 0.2.1.  Easy to change if not acceptable.