Have data.fetch use gwpy option for both realtime and historical frame fetching

This will automatically choose between the different types (shm vs. datafind) depending on the time in which analysis is done. I have set the time to switch based on gps_now - gps_start < some_latency. I have set this latency to be 70 seconds.

Note: It will cut out some data in the front for the time being because we actually request 75 seconds of data and there is like 70 seconds stored in /dev/shm/ but it's better than nothing. If we can request the stored frames in /dev/shm/ to extend to say, at least the time until they are available through some other method like datafind then this will be hunky dory.