renamed fetch -> fetch_nodes

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
added fetch /packages

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
added fetch to specific /package/xyz

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>
improvement: unified error reporting in restangular fetches

Signed-off-by: Dominik Richter <dominik.richter@gmail.com>