point to the version xml of stable releases

update JREs

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

show the right license in the license dialog

for stable releases mucommander.com/version/version.xml should be used