Things like conversion between some controls and the yaml config file
etc ...

* inst/rmd/app.Rmd: Shinyscreen GUI.

Extraction tab contains error input widgets that take error in the
+/-, so as the half-width of the interval centered on the value.

A new kind of control was produced that inlines the text of labels
with the input box. Another variant places two labels around the input
box (suitable for units).