Combine 13 functions into two

Combine 8 functions to get stations with data into one
Combine 5 functions to get number of events into one
Make one function with the usual flexible date criteria
Also make data type (events or weather) an option for stations_with..
Fixes #42 by using the sums of the histograms based on ESD
Change download form text to inform all data from 2013 is available