Need to allow single tag for different modes in a single set

At this point, the flow is entirely reactive, starting from the file inputs.

Added note about RT, added Win/RStudio install info

But, plotting does not work for MS2 chrom and spec

In the last couple of commits, the application has become much more
reactive. I have focused on throwing out as many as possible important
observers in favour of render/reactive environments.

As a consequence, the application is much more responsive to change
and updates properly almost all the time.