Hyper-V VM connection, bug fixes

• support of Hyper-V VM direct connection (extension of the RDP protocol; doesn't require remote desktop access to be enabled on the guest VM) (thanks jol64)
• updated documentation for usage and limitations of the Hyper-V connection
• fixed a potential inversion of arrows and numbers keys (whatever the numlock status)
• fixed a path issue for the myrtille PDF virtual printer (in debug build or if the printer service runs under a custom account)
• fixed the files popup which always downloaded the first document, regardless of the selected one (regression from version 1.9.0)