domain instead of IP

refer to de88a114dcf8b4 in libertree-client-rb
build rpms/debs for all components at once

FPM can build rpm and deb packages from our gem dependencies.
FPM should be installed with:

  gem install fpm

The Gemfile contains a list of all runtime dependencies for all Libertree
components (except the frontend).  We collect all dependent gems with bundler:

  bundle install --without development --path vendor
  bundle pack --all

The dependent gem packages are configured to install to /usr/share/libertree/gems;
the backend libraries, config files and scripts will be installed to
/usr/share/libertree/backend-rb .

TODO: build packages for the frontend
split regular gems and those that build extensions
Merge branch 'master' into xmpp
recommend Bundler and the use of the system Ruby package
send along origin domain instead of public key
Merge branch 'master' into xmpp
Merge branch 'master' into xmpp
Merge branch 'master' into xmpp
add explanatory comments
force build from local gem; do not download
generate-key-pair script name has changed
add section comments
bundle install is not needed
model version has changed
update eventmachine dependency
make gem dependency of rpm/deb
set package name
default target is libertree-backend-x.x.x.{deb,rpm}
make built rpm/deb packages prerequisites for libertree-backend