Initial Remote Assistance Support

[MS-RA] basic implementation
[MA-RAI] .msrcIncident file parsing
[MS-RDPEMC] complete implementation

How to use: create an invitation.msrcIncident file from the novice computer (msra.exe /novice). Send the file and password to the expert. Launch xfreerdp with the file as the first parameter, and give the password as a command-line parameter (/assistance:2FW2Q8796HV8). The screen will be black until the novice accepts the connection. To request/release control, use ctrl+alt+c.

This has been tested with Windows 8.1 as the novice computer.