Added Plesk-Driver to Password-Plugin

This Driver allows to change Passwords via Plesk RPC-API
fixed typos and added section in README
Merge branch 'master' of https://github.com/roundcube/roundcubemail

Conflicts:
	plugins/password/config.inc.php.dist
Fixed merge conflicts
removed unwanted file
Merge pull request #187 from adfinis-sygroup/master

Added Plesk-Driver to Password-Plugin