Various improvements

* 553cc53 and fd7bb4e &mdash; Upgrade APScheduler to 3.0. Different API, but as soon as the #1955 gets merged/is finished, I can reconfigure the jobs on config save.
* 2ddb96e &mdash; Clarifies logging (e.g. for #1957)
* 8a88215 &mdash; Fixes #1948
* 6b4afd8 &mdash; Fixes #1926. Converting torrents is an option. Also cleaned up some searcher.py code.
* The rest: several small changes and additions.

Runs under Python 2.6.9 and 2.7.8, but haven't tested it thoroughly yet.