rework of runcommand.sh
* now takes into account current aspect ratio of video mode to avoid choosing the wrong aspect ratio on 4:3 monitors
* removed unused video mode selections - users can specify an exact mode should they wish to:
* short 1 second delay before resetting framebuffer, to avoid screen being left in unusable state
* only changes the video mode if the new screenmode differs from the current mode

runcommand is called with two parameters - reqmode, and command. reqmode can be:

reqmode==0: run command
reqmode==1: set video mode to 640x480 (4:3) or 720x480 (16:9) @60hz, and run command
reqmode==4: set video mode to 1024x768 (4:3) or 1280x720 (16:9) @60hz, and run command

reqmode=="CEA-#": set video mode to CEA mode #
reqmode=="DMT-#": set video mode to DMT mode #
reqmode=="PAL/NTSC-RATIO": set mode to SD output with RATIO of 4:3 / 16:10 or 16:9

note that mode switching only happens if the monitor reports the modes as available (via tvservice)
and the requested mode differs from the currently active mode
added custom screenmode switching support to runcommand.sh. if a hotkey is pressed before the emulator is loaded (x or m currently - originally just m - but x added to be helpful to picade users)
a dialog is opened up where a screenmode can be selected. the setting is then saved for the current binary being launched (in /opt/retropie/configs/all//videomodes.cfg).
fixed typo / split fbset onto two lines
use just path/binary for video mode setting
added ability to set video mode on a per rom basis
use case/esac rather than if/elif
uncomment clear
simplified code to strip brackets to 1 line
fixed cancel on first video output configuration menu
changed wording of first menu title
Merge pull request #532 from joolswills/runcommand.sh

rework of runcommand.sh