Rebrand family of report_data() functions

[BBieri]

Create a family of report_data() functions that serve the following roles:

• What is in this package/database/dataset?
  • Will contain the names of the content and the bibliographic information
• How do the datasets compare within one structure (package, database, dataset)
  • This function will contain information about missing values, number of observations, number of variables, earliest beg date and latest end date.
• How do the datasets compare to the original dataset?
  • This function will compare the evolution from the originally imported dataset to the final product we display in our packages to ensure transparency.
  • This will contain information such as the link to the original datasets, the original coding variables, etc.
  • See Issue Create a data_evolution() function that contrasts the processed (and exported) datasets to their original versions #134 for more informations.

The names of the functions are tbd. I welcome suggestions :)

[BBieri]

• data_source()
  • Will contain the names of the content and the bibliographic information
• data_compare()
  • This function will contain information about missing values, number of observations, number of variables, earliest beg date and latest end date.

[BBieri]

The data_source() and data_compare() functions are mostly done. Their development is now held back by decisions on the "qID" issue, e.g. which column should be considered as the ID.

Please let me know your thoughts on the function names, the output (do you want to display other information?), as well as your general feedback on the functions.

Sidenote: I will create a separate issue for the data_evolution function since it is less of a priority for the moment. You can find it here: #134.