Merge pull request #104 from TazeTSchnitzel/serverplugins

Added server plugins support (plugins server asks client to use)
Merge remote-tracking branch 'remotes/ajf/serverplugins'
Merge remote-tracking branch 'remotes/ajf/serverplugins'
Improved warning message when the plugin download prompt is disabled
Beta release preparations
Added Server-sent plugin networking, aka PluginPackets!