Refactored unknown contact picture generation

Introduce drawTile method in order to remove code duplication
further improvment trying to deal with large images
Merge branch 'development' of github.com:siacs/Conversations into development
added missing strings
write contacts on system shutdown
fixed #136
implementet missing methods on the new roster mgmt
Galician translation
offline crud of contacts
Contact details translations + update spanish translations
Merge pull request #144 from kruks23/development

Contact details translations + update spanish translations
Merge pull request #143 from nachovfranco/mycommits

Galician translation
updated readme
code cleanup
fixed possible npe
end otr sessions earlier / more often. can lead to unesessary handshakes but can improve reliabilty
Title activities translations + contacts translations + update Spanish Translations
Merge pull request #145 from kruks23/development

Title activities translations + contacts translations + update Spanish
More harcoded translations + Spanish
Merge pull request #140 from strb/mucicons

Refactored unknown contact picture generation