Add existing weights file and mapping files to package

[JSchoenbachler]

I think this would be best accomplished using the data folder which would make data available in the package by default.

Example of this being done in deltaccd: https://github.com/hugheylab/deltaccd https://github.com/hugheylab/deltaccd/tree/master/data https://github.com/hugheylab/deltaccd/blob/9e48960017120d952472b42824b9349351ade31d/R/deltaccd.R#L292-L308

R Packages reference: https://r-pkgs.org/data.html

[arefnel]

26683aa246a9d4625e941ebaa3742c7699553c4e

• added the weights file to data/
• added an argument to getWeights() for returning pre-calculated weights