Add time series and FFT plotting

- Method added to 'ReducedBScan' to cast data into time series
- Internally relies on a new 'file_index' column
- Add 'timeseries' flag to many plot methods

- Add AB frequency range indicator to 'plot_fft'

Signed-off-by: Dustin Ngo (Mac Pro) <dustin.ngo@gmail.com>