use If-Modified-Since on getting alltags.json
use If-Modified-Since on getting alltags.json

so it will only download a file if it is newer than
what is embedded or in cache

and only requires 1 webRequest

ermshiperete/libpalaso,gmartin7/libpalaso,ermshiperete/libpalaso,gmartin7/libpalaso,ermshiperete/libpalaso,sillsdev/libpalaso,ermshiperete/libpalaso,gmartin7/libpalaso,sillsdev/libpalaso,gmartin7/libpalaso,sillsdev/libpalaso,sillsdev/libpalaso