Refactor UI and Server files into Modules

[christophertull]

Right now the different UI tabs and charts are all copy-pasted and suffixed with numbers (e.g. df_plots1, df_plots2, etc). This is fine for the short term, but it will make the code more readable, and maintainable if we refactor these into Shiny Modules and then generate them in a loop.

See here for info on creating modules: http://shiny.rstudio.com/articles/modules.html

And here for generating a UI in a loop: http://shiny.rstudio.com/gallery/creating-a-ui-from-a-loop.html

[christophertull]

closed by #33