use https sources in Gemfiles and also in the documentation (#4109)
include Gemfile.lock to prevent unintended updates (#4174)

We had a broken production server lately because it had upgraded the couchrest model dependency to one that had a different naming scheme for a function we overwrite. So that broke production.
Let's prevent that by including the Gemfile.lock in our repositories.
fix download urls for mac, android and windows

They did not point directly to the download.
remove duplicate source line that was using http

I don't think we need to list the sources again in common_dependencies.rb
use osx not mac as an identifier for the os.
adopt css to mac-> osx change
the class for the html tag is linux32 - not just linux
Merge remote-tracking branch 'origin/master' into develop
Merge branch 'feature/4109-https-sources' into develop