Rewrite data loader

[markhalonen]

The data loader and data interpreter should be broken apart. They are intimately intertwined.

Data loader jobs:

1. Pick a frame delimiter and a datapoint delimiter. That's it.

Data interpreter jobs:

1. Label the columns that come out of the data loader. Must select time or frame rate first.

Once the data loader is rewritten it can get used in the fitter. Maybe write it for the fitter first.