Merge pull request #69 from anryko/master

Backend code review and cosmetic fixes
Fix breaking grouping by duplicate node entries.
Finally make power edges work.
Allow deleting nodes. Moves 'Add Node' together with removal feature into own list view.
Sort node list in 'Manage Nodes' view.
Suggest node names from internal IPs known to NSS
Avoid race of suggestion and node list.
dirty workaround, sometimes auto-grouping causes group without leaves which causes an Exception, which we do not want
Use no-cache for /nodes and /nodes/suggestions to have always up-to-date lists.
List agent connection errors in report.