Reduce messages overload

Show only the last error if there are multiple.
Merge pull request #209 from dimagi/109014-error-popups

Reduce messages overload
Preserve whitespace during XML serialization
Merge pull request #210 from dimagi/109032-line-breaks-in-hidden-values

Preserve whitespace during XML serialization
Fix barcode icon

FB case 109900
Merge branch 'master' into develop-fixes

- Refactor XMLWriter patch
- Tabs -> spaces in util.js
- Regenerated vellum.min.js

Conflicts:
	src/js/util.js
Merge pull request #211 from dimagi/develop-fixes

Develop fixes