allow raw data with peak tables in iso_prepare_continuous_flow_plot_data

[sebkopf]

re-arrange the zoom and other calculation in such a way that iso_prepare_contionuous_flow_plot_data can be implemented as an S3 method that can take a raw_data (+/- peak_table) trace and work with it directly to ensure compatibility with pipelines that move away from iso_files and work with the raw and peak table data directly.

note that this might mean it will be easier to do the gathering of the data trace data at a later point also in the iso_files version of this function (i.e. iso_get_raw_data without direct gathering at this early) point and then we could deprecate the data_trace paramter in iso_combine_raw_data_with_peak_table and just have a separate gather function for raw data that works outside of the iso_get_raw_data as well.