Make a graphical interface

[Guillawme]

This sort of defeats the purpose of having a command-line tool, but can be valuable if it's still simpler to use than a spreadsheet program.

Ideally, the user would simply drop a (properly-formatted) data file, indicate names of blanks and titrations data series, and get the result table and final figure immediately.

Shiny seems well suited for that.

[Guillawme]

A big advantage over spreadsheet programs would be to have this interface be able to perform batch processing over many data files.

It should print out a report with result tables and figures for individual datasets, as well as aggregated results (average Kd +/- standard error, number of replicates, and a single figure with all datasets on a relative scale as average points and error bars, plus the fit curve; see #12).

[Guillawme]

Using ggplot2 for figures generated by the command-line pipeline works well. For the Shiny app, it would be nice to have interactive figures made with plotly. This adds a dependency, but would make the GUI much nicer.