add handler for Google Fit data

`Fit/Daily Aggregations` csv files -- started appearing in 2017

`Fit/Activities/*.tcx` and  `Fit/Activities/Low Accuracy/*.tcx` files -- perhaps worth just having a function to get them, something else should actually handle tcx files
also a bunch of them seems to have disappeared in 2020 (comparing with 2018) -- not sure if it's some sort of retention
