Token exchange performed to get offline token for API access.
Added general settings option to specify a comma delimited list of allowed video file extensions to be checked against existing files when performing show updates/refreshes
Added database test case. Fixed TV episode database upsert code. Misc variable name cleanup.
Improved memory usage from database calls. Misc code cleanup.
Fixed issue with failed downloads history view when history item's provider is no longer enabled or present.
Fixed issue #261 - skip download button not enabling save defaults.
