IFAR Table Changes

added 'lookback' in yaml to be in ifar table schema. this simply goes gets data from now to now minus the lookback (seconds). changed how update_data works in scald.js and so it should actually work now. correctly adds y values (1,2,3...) now depending on how much previous data there is. changed how _draw in scald.js works for ifar only and it needs to recreate the entire plot (newPlot) for plotly reasons. in serve.py i changed how 'far' is entered as an arg into retrieve_triggers, forced into a float. added 'far_key' in yaml to be in ifar table schema. it will look for this instead of the default 'far' if found in the yaml.