Method 'yii\mail\MailerInterface::compose()' reworked allowing rendering message body.

fixes #1146

not needed when installed via composer and application config loads
composer extensions correctly

- setter methods renamed to have pure name
- method 'createMessage' renamed to 'compose'

set alias to the correct path as they are not part of the yii framework
directory anymore

Fixes #1133: gii controller generator now uses application controllerNamespace as default value for "Controller Namespace"

fixes #1131

fixes #1132

updated read me.