* Update Roundcube docs page going from 1.5 to 1.6
This is to update the docs page to install or upgrade to Roundcube 1.6.0 along with the needed 'sed' commands to make any necessary config changes going from 1.5 to 1.6
* Decline auto local config fix
If you allow the update tool to upgrade your config file, it doesn't do it correctly, so we're better of doing this our self with 'sed'
* Update roundcube 1.5 to 1.6 DE instructions
* 'smtp_server' to 'smtp_host' in config example
