Merge pull request #789 from svetlemodry/development

Czech translation updated
fixed #755
Merge branch 'development' of https://github.com/siacs/Conversations into development
Update spanish translations
Merge pull request #797 from kruks23/translation

Update spanish translations
Merge pull request #794 from svetlemodry/development

Czech image transfer string fix
inject ui callback into running mam query
fixed another break continue bug
don't include empty fingerprints in list of otrfingerprints
more null checks for otr fingerprints
get rid of special self presence object and incorporate that into roster