Kobo importer fixes and more translation titbits

Fixes:

• https://aptivate.kanbantool.com/b/437721-internews-hid-2018#20363239
• https://aptivate.kanbantool.com/b/437721-internews-hid-2018#20363157

Going from Pula experience, we want the importer to always run, even when we get weird data. Then we should handle this on the importer layer. This will save heartache for users because they'll have these huge sheets and won't know half of what is in them, I assume. So, I make the body field optional, handle this in the importer and show a red 'Missing text' on the view/edit table view when you want to select that item. Before this, the importer was taking in a None type and converting it to None, as in text.