Reformat default data sets

[solveigvandervegt]

The default data sets describing demographics and cases for different countries are currently in a different file type than the excel files from which this information is taken if the user does not wish to use the default data sets. To avoid having to comment/uncomment lines in the code when switching between the two, it would be useful to put the default data in the same format as the up-to-date data so both can be processed in the same way in the R code.

[solveigvandervegt]

Update: the plan is to write a function in R that takes a country (chosen by user) and fills out the excel template file for this country. The cases, mort_sever, and population data for the specific country is loaded from the default files. This will allow for the streamlining of the parsing of parameters and data afterwards, as it will now only need to be done from the excel template. It will also prevent individual users from introducing typos, etc. in the template file.