Clocktools sample trace

[ZhuokunDing]

1. Reorganize fetch_timing_data into:
   • scan_image_correction: fetch delay for the entire field or a single unit based on the argument scan_key
   • fetch_timing_data: fetch the corresponding timestamps based on the argument timing_type
   • interpolate_timing_data: interpolates the timestamps from the source timestamps to the target time stamps and vice versa.
2. Add time-stimulus as an option in interpolating_timing_data to load flip times in stimulus clock. The current implementation concatenates the flip times found in stimulus.Trial, which is not necessary since concatenated flip times already exist in stimulus.Sync.Syncmodel. However Syncmodel tables are not populated for the platinum scans yet. The current implementation should be updated after the Syncmodel tables are repopulated for the platinum scans.
3. Implement sample_trace using fetch_timing_data, interpolate_timing_data and interpolating_signal_data to sample the traces at arbitrary time points in stimulus time. This function could be extended to sample with behavior time as well, not implemented at the moment.