add. secret key variable to settings for signing session cookies in flask-login.
mod. renamed request parameters "date_start" & "date_end" to "start" and "end" respectively
mod. "build_key_signature" convert request values to string when building each key
mod. move HASH_KEY_DELIMETER into data module, revise key.
mod. change "period_type" parameter to "group", both in metrics and in api
rm. lingering refs to "restrict" param
fix. how data is referenced and hashed for requests.
mod. use a hash of key signatures for all responses.