Optimized the TV show scanning logic

Fixes #25

Moved the call to retrieve the TMDb config information out of the download tasks and into the GetFilesTask. This ensures that this network call is only made once instead of getting called each time a download task is executed. Refactored the TV show fetching logic to look in the db first before making network calls to get a TV show. Together, these changes have helped the TV show logic go from being able to process roughly 4 shows a second to 7.