Update TorrentManager docstrings and remove old load_torrent method

Passes flake8 and mostly passes pylint
Use true division 'from __future__ import division'
Fix move storage dialog not closing
[#637] Add a Moving storage state along with progress

Uses attr Torrent.moving_storage for now but can be replaced with
future lt1.0 status field.
Refactored the code to use the common.TORRENT_STATE list.
Added a translating dict to ui.common to aid translation of state text.
Show actual error in status from storage_moved_failed_alert
Fix typo in loading peers_tab state
Change logging of 'creating backup' to debug level