v0.19.3 hotfix release

The update will include the following changes:

• better email queueing and logging and more informative errors (some users still reported breakage without useful error messages)
• we now default to testing email accounts after any change and don't send emails if we know an account is setup incorrectly.
• generally better logging of what happens in a run
• some users saw dupes in the user overview. these were only displayed in duplicate there, not causing any functional problems, but of course needed to be fixed.
• a lot of users found the current handling of missing values in surveys in formr counter-intuitive. two changes here:
  • if a check-type item is unchecked it defaults to 0, not NA
  • using the R function is.na(item) now also works in Javascript (formr just replaces it with the approximately correct and hard to remember JS idiom (typeof(item)==="undefined")
  • one note: is.na in javascript will not throw an error if the item name is mistyped. it's a limitation of how we set things up. I still hope this causes fewer problems than the old way.