[R] Fix function and unit testing bugs

[gsvidaurre]

score_clusters() has hardcoded timezones argument values in different sections that need to be updated from "America/New York" to the value provided to the tz argument, or just "". Fixing the timezone argument so it accepts geographic/location information should be a future focus.

[gsvidaurre]

Originally issue #477: Fix the following in unit tests:

The path for unit testing needs to be generalized, ideally in the main script to run all unit tests
The code to install packages if they're not already installed should updated to:
is_installed <- function(p) is.element(p, installed.packages()[,1])

invisible(lapply(1:length(X), function(x){
if(!is_installed(X[x])){
install.packages(X[x], repos = "http://lib.stat.cmu.edu/R/CRAN")
}
}))

[gsvidaurre]

Also fix a bug in detect_perching_events(), in which the function fails to detect two empirical RFID detections around 1.5 seconds apart, even using thresholds of 1 or 2 seconds.