Do cleanup work in an earlier stage to ensure correct conf saving.
Preview now correctly uses the selected file. Closes #1222 #1182.
Allow to resize the columns in Add New Torrent dialog. Closes #1207 #676
Ensure that at least one column in the tranferlist is always visible. Closes #1165.
Ensure that the options window will always be placed onscreen. Closes #1226.
Delete temporary after they aren't needed. Closes #1188.
Correctly detect libtorrent version.