Improvements to imports

[efg]

When a form is imported, if a column is missing, an error occurs. Sometimes, depending on what is imported, this can be a Rails error. This should be fixed.

Also, it would be more user-friendly if a user could just import a list of users, participants, topics, etc.; the system would then display what was imported, and let the user choose from a dropdown which field was which. The default ordering would be the same as what is currently required by Expertiza. I've seen this in a number of other educational apps. Would be nice to have it in Expertiza.

Includes issues #13 and #52.

[ghost]

This is in E213 - not clear if that has been merged.

[yangsong8]

E1656 rejected.

[efg]

This functionality has been implemented in Project E1776, and seems to work. However, the messages on the Participants page are out of date (they don't refer to choosing columns via dropdowns), and on the import page, the text is really ugly.