[BACKPORT] Use unicode csv writer
Fixed github issue #624: UnicodeDecodeError when exporting orders as CSV
Remove BOM from CSV writer

It was causing problems with Excel, which didn't recognise it and showed
a strange symbol.  I can't find a compelling reason to keep it, so it
goes.
Bump version to 0.4.12
Merge pull request #1057 from tangentlabs/release/0.4/backport/unicodecsvwriter

Release/0.4/backport/unicodecsvwriter