Workflow restructuring

The current serial workflow of "decay search" (DescriptorSearch) -> "select lines and datasets" (LinesTable) -> "configure DecayTreeTuple" (SelectVariables) is not optimal.

I propose that the main page be what is currently LinesTable. The user should always be able to come back here, and this should be where all of the output is downloaded from. A button should be added to create a new row in the table, then when you click the empty "decay" box, it opens DescriptorSearch. Once a decay is chosen, a DTTConfig object is immediately created, and a button on the row can be used to bring up SelectVariables to configure it. Updating the choice of lines in LinesTable should immediately update the inputs list in the DTTConfig.