Add grace-period to bypass the local tvdb show status 'ended' check.
The bypass introduces a sliding window of +/- 30 days from the latest aired EP airdate and -30 day before next unaired EP airdate where we will get the latest data from tvdb. We exclude season 0 at this time from this check to prevent abuse. This should prevent the need to do 'force full update' to fix shows that get their status changed incorrectly while still reducing the hits to tvdb for shows that are in-fact ended.
Added 'ended' bypass on every full backlog (3 weeks-1day) to prevent older shows with no next aired ep from being missed (ex Arrested Development or shows that have a solid year or more between seasons - like Sherlock)
Change variable names, remove try and len
Change logic and flow and put decisions into should_update

return faster
calculate today once
Add last_update_tvdb for controlling nigthly updates

+ move setTVRID into own try for correct error log message
Minor DB corrections.
Fix exception on last_update_tvdb being empty
Add default value to existing database
Change if last_update_tvdb is older than 90 days.. we update