Include X2Go plugin

Description

I Daniel, a employee of Mike Gabriel (sunweaver) rebased the X2Go plugin for Remmina to the latest master.

I am currently working on adding new settings which are supported by pyhoca-cli but are not implemented in the plugin yet. (Like audio support or quality settings)

The ultimate goal would be that the X2Go plugin works on wayland without a compability layer of some kind. It currently uses a X11-Only (XEmbed) feature to embed a pyhoca-cli window into the Remmina window.

Related Issue

Following issues are related: #17 (closed) #1925 (closed)