Fixed issues from data source updates

Updated app.R to address breaking changes in COVID-19 Data Hub v3.0.0.

Initial release

Changed scaling to "X per 100,000 Population"

- "Cases/Deaths per 100,000 Population" now used for scaling instead of
  "Cases/Deaths per capita"
- Default time interval is now 180 days before latest data update
  instead of 60 days
- Full country names now used in graph legends
- Axes swapped on animated scatter plot
- Animated scatter plot now has a more descriptive element title
- Shiny dashboard sidebar is now displayed by default
- rsconnect/ directory is now included in repo
- Comments added to app.R to make brackets easier to follow