Application menu fixes

Remove latency-plot as an Application menu item as it doesn't work for
a system which has _only_ a RIP build because the environment for
execution of commands from the Application menu is limited.
(unaware of linuxcnc RIP vars, for example, package require Hal fails)

Provide an alternative point-and-click access for latency-plot,
latency-histogram:
  Since demo scripts in configs/apps/ are invoked from the main script
  (scripts/linuxcnc) where more environemntal vars are available
  these programs are modifed to work for a system with only a RIP build.

also:
  For RIP only system: make configs/apps/xhc-hb04 demos work
  Renaming for variable EMC2_SCRIPT
  Improve pyvcp_demo exit handling
  linuxcnc_info use editor search
  app scripts: prepend auto_path (RIP, gui usage)

Signed-off-by: Dewey Garrett <dgarrett@panix.com>