Add sysinfo() flags for R Commander, RKWard, and SciViews

[HenrikBengtsson]

Add sysinfo() flag specifying whether R runs in various environment or not:

• [x] rcmdr/rcommander - R Commander
  • Comment: this is not really possible to detect at startup, because its GUI is opened when library(Rcmdr) is called. /HB 2019-08-29
• [ ] rkward - RKWard
  • Notes: Attempted to install on Ubuntu 18.04 using sudo apt-get install rkward but run into problems of unmet dependencies on r-api-3.4.
• [ ] sciviews - SciViews