bugfix issue #10 (putatively because the reported issue didn't seem to be real)
handle case where user doesn't upload a excel file
address issue #5: Convert Excel date float into string for form processing. Adapt description in Excel templates.
add preparedBy -> User field to all Sample models
preparedBy support in upload tables. Autogeneration if left empty.
data migration for new preparedBy column in Sample
Merge branch 'master' of https://github.com/graik/rotmic