Add support for config files based on labels in processing workflow

[ghost]

In some cases, users may want to reprocess thier data with different parameters (ie comparing filter settings or differentiation methods) and gmprocess stores the config file that is read during gmprocess process in the ASDF file for optimization reasons. This means the user needs to run gmprocess assemble -o each time the system config file is changed before running gmprocess process -l mylabel

In order for the labels to work so that users can modify the system config file and then rerun only gmprocess process -l mylabel the ASDF file should support label-based config files. This means each label would have its own config file stored in the ASDF file with whatever processing parameters the user requires. In most cases, this should result in only few labels (for different processing parameters) with a few config files in the ASDF file.