speed up overflows plugin?

The overflows plugin is currently slowest, clocking in at a little over a minute. It looks like it's redundantly calling gwpy to pull data, presumably for different channels all at the same time. This could probably be sped up considerably with a single gwpy fetch call for all channels at once.

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018-10-17 13:14:43,547 executing followup: find_overflows(1223824132)
2018-10-17 13:14:43,547 plotting WIDE ADC overflows for ASC subsystem
2018-10-17 13:14:43,547 DATA_ACCESS: gwpy
2018-10-17 13:14:48,212 DATA_ACCESS: gwpy
2018-10-17 13:14:51,234 DATA_ACCESS: gwpy
2018-10-17 13:14:53,959 DATA_ACCESS: gwpy
2018-10-17 13:14:56,703 DATA_ACCESS: gwpy
2018-10-17 13:14:59,221 plotting WIDE ADC overflows for OMC subsystem
2018-10-17 13:14:59,222 DATA_ACCESS: gwpy
2018-10-17 13:15:02,147 DATA_ACCESS: gwpy
2018-10-17 13:15:05,270 DATA_ACCESS: gwpy
2018-10-17 13:15:08,117 plotting WIDE ADC overflows for LSC subsystem
2018-10-17 13:15:08,117 DATA_ACCESS: gwpy
2018-10-17 13:15:10,612 DATA_ACCESS: gwpy
2018-10-17 13:15:13,763 DATA_ACCESS: gwpy
2018-10-17 13:15:16,820 plotting WIDE ADC overflows overview
2018-10-17 13:15:17,918 plotting ZOOM ADC overflows for ASC subsystem
2018-10-17 13:15:17,919 DATA_ACCESS: gwpy
2018-10-17 13:15:21,355 DATA_ACCESS: gwpy
2018-10-17 13:15:23,786 DATA_ACCESS: gwpy
2018-10-17 13:15:26,229 DATA_ACCESS: gwpy
2018-10-17 13:15:29,316 DATA_ACCESS: gwpy
2018-10-17 13:15:32,051 plotting ZOOM ADC overflows for OMC subsystem
2018-10-17 13:15:32,052 DATA_ACCESS: gwpy
2018-10-17 13:15:35,362 DATA_ACCESS: gwpy
2018-10-17 13:15:38,374 DATA_ACCESS: gwpy
2018-10-17 13:15:41,019 plotting ZOOM ADC overflows for LSC subsystem
2018-10-17 13:15:41,019 DATA_ACCESS: gwpy
2018-10-17 13:15:43,742 DATA_ACCESS: gwpy
2018-10-17 13:15:46,328 DATA_ACCESS: gwpy
2018-10-17 13:15:48,752 plotting ZOOM ADC overflows overview
2018-10-17 13:15:49,597 analysis done.