use file extension of uploaded xlsform
test for xlsx xlsform download
Merge branch 'master' into xlsxdm

* master:
  Fixed tests to expect _uuid and _submission_time columns
  Added optional arg to make_submission to overide submission time for fixtures testing
  Updated README with utf8 note
  Added xls export fixture
  Added _uuid and _submission_time to xls export
  Added _uuid and _submission_time to csv exports

Conflicts:
	main/tests/test_process.py
explicit call to _publish_xls_form
Merge branch 'master' into xlsx_xlsform_download

* master:
  Extra at sign on twitter handles specified with an at sign
Merge pull request #988 from modilabs/xlsx_xlsform_download

#984 allow xlsx xlsform download