Runs a Linear regression on the data and returns it in a form to be merged in the runRegressionAnalysis function
regressionInnerLoop(Formula, DF, Keep = NULL)
a row of a DF containing the site, last date, timespan, number of rows, model slope and significance, and predicted percent change, and what linear model was used
LM model to be fit on DF
Contains the data needed for Formula to work
The col in the original DF to keep besides Date