Move plugins into their own plugins folder.  Change addSchema method to install, add uninstall method to Manager call and use plugin for install/removal rather than directly in PluginManagementPage

git-svn-id: https://svn.code.sf.net/p/freeghost/code/trunk@1711 71f96598-fa45-0410-b640-bcd6f8691b32
ADD README File.