Add option to disable idle timeout

[Marc4129932]

On RDP settings, there are static options without much description. The source code mentioned 600 being the maximum on idle timeout, but it also enforces a value between 10 and 240.

I would like the option to never disconnect for being idle. I'm usually connected to servers 24x7 running something, and I don't want to have to re-login over and over.

I tried using 0 (zero) and -1, but found it was forcing it to 10.

The application works great for me otherwise.