fetch missing avatars from server
Merge pull request #339 from kruks23/development

Update Spanish Translations + gallery
fixed problems with sha sum calculation on avatar write. delete avatars with non matching sha sum
Merge branch 'development' of github.com:siacs/Conversations into development
bug fix for not working notification grace period in muc
fixed #320
save images to external storage instead of internal. this requires more permissions. fixed #150 fixed #177 fixed #333 - this might need some more polish though
more fixes for notfication in conferences
grant uri permission on share picture
ability to bring default picture back with long press in publish avatar
bug fix for 'back to default'
added warning lable if server doesn't support pubsub. refactored feature identification into seperate class
fixed very rare npe
show add to roster dialog when trying to start otr session
trying to fix activity has been destroyed error
work around xml parser issues...
changed all displays of avatars to be center crop instead of fitXY
potential fix for rejected execution exception
fixed rare npe after race condition
added limited private muc chat feature (messages are now properly marked) - long press on user icon will sent private messages. fixed #259