avoid posting empty comments

fix Jasmine test

updated changelog with bugfix #3836

fix changelog update

remove wrong bug fix line
Merge pull request #4008 from pestrada/3836-avoid-empty-comments

avoid posting empty comments
fix XSS vulnerability in conversations#new, closes #4010
Add the ability to upload photos from the mobile site
Merge pull request #4004 from movilla/upload_photo

Upload photo mobile. Close #3324