MOBI Input: Dont crash on corrupted JPG images

Use ImageMagick instead of PIL, which handles corrupted JPG files
better. Fixes #1404590 [calibre misbehaves when bad jpeg in mobi file](https://bugs.launchpad.net/calibre/+bug/1404590)
Apparently there exist a lot of Macs out there with completely broken permissions on the home folders. Workaround that.
Allow name manipulations to be performed without a full container object
Refactoring
Pass through tracebacks that occur while getting data
Use openntpd instead of ntp