Add scripts to fetch dependencies

./build.sh will install RouteFlow's dependencies from debian packages or
source (releases or git), and fetch alternative RFProxy implementations
from remote git repositories. It then bootstraps, configures and builds
all of the RouteFlow components.

Signed-off-by: Joe Stringer <joestringernz@gmail.com>
Add configuration option for rfproxy git branches

Signed-off-by: Joe Stringer <joestringernz@gmail.com>