Refactor input gatherer

[lovelysandlonelys]

• still ingest all the series it needs to ingest from the series provider
• but then has a second step that checks for post processing steps and instantiates each class in the right order from the dspec to post process the data collected

Notes

• remove dspec parser into it's own class
• three separate processes (noted in dspec task)

[lovelysandlonelys]

Notes/Improvements:

• Pass only the series that postprocess call needs to compute the out keys when making the post process call rather than the entire input vector
• Check if there is a different method that doesn't handle collisions with combining dictionaries (rather than dict.update(dict))