plot method of SnglBurstTable uses a fraction-of-a-second reference time

Created by: tdent

For me (on ligo-la) this results in an x-axis with a fraction-of-a-second reference time (i.e. time in minutes from that time) and having the first axis tick at a fractional value, i.e. -2.98..... e-07 minutes.

sep15trigs = SnglBurstTable.fetch('L1:GDS-CALIB_STRAIN', 'omicron', 1127217617,1127239217)
oplot = sep15trigs.plot('time', 'central_freq', color='snr', edgecolor='none')
oplot.add_colorbar(clim=[3,50], label='SNR', cmap='hot_r')
oplot.savefig('public_html/detchar/ER8/ETMY_bounce/Omicron_STRAIN-Sep_15_12:00_18:00.png')