Images for series and seasons are now optional and are automatically fetched, if they were previously missing.
Fixed an error that occurred, when a series has no season 0 (which for TMDB is normally the specials).
Redid the frontend with Bootstrap and an easier template API.
The users login is now consistently displayed among all frontend pages.
The frontend now keeps track of the currently opened page.
Only throw an exception (causing the task to be re-scheduled) if there was a connection problem. Excludes JSON-parsing errors.
Explicitly allow null-values for most dates.