Update strings.xml

swipe horizontally
Merge pull request #406 from MklBst/master

Update strings.xml
Bump version
Update grammar versions
Update changelog
Update test list
Merge branch 'release/0.31.0'
Merge tag '0.31.0' into develop

* Enhancements
  * Minor text update
* Bug fixes
  * Fixed crash in results activity when results couldn't be downloaded
  * Hide "erase my data" button until it's really implemented
  * [#407] Morning poll appears multiple times