identify Haiku operating system

store credentials to Google Drive in GoogleDriveClient

minor changes in the readme file

point to the version xml of stable releases

bump build number

fix windows packaging

change the default macOS

fix mucommander#61: open the 'This file may be too large for this ope…

…ration' dialog at the right place

upgrade nebula.ospackage to version 5.1 to produce valid rpm for fedo…

…ra >= 28

readme: minor changes