New screens for network nodes.

[germanferrero]

With libremesh/lime-packages#873, we now have the possibility of showing in the LimeApp:

• Network Nodes: The list of network nodes ( currently reachable or not ), to quickly find a node by hostname and find out basic data about it.
• Reachable Nodes: The list of reachable / unreachable nodes. To get a picture of which nodes can be reached from yours, and help in diagnosing issues.
• Upgraded Nodes: The list of upgraded / not upgraded nodes. To know which nodes are running the last version of the firmware and which are not (based on eupgrade config).
• Remove Nodes: We also need a password-protected screen to purge old nodes from the list so they do not appear at the unreachable / all nodes list for ever.

The current proposal is to add one screen, with it's corresponding menu item for each of the above items.

[germanferrero]

This proposal is currently implemented at: #310.
But, we have put it on hold until we solve some concerns that arose while implementing it:

• The screen of network nodes and upgraded nodes would show only the nodes updated to some firmware version which includes Add shared state network nodes lime-packages#873, this could confuse users. May be we can plan an upgrade path to minimize the impact of it, or add a legend to clarify.
• The screen of reachable nodes determines reach-ability on top of shared-state nodes-and-links db, which is not always up to date. A node can be there in the db but not reachable over IP and vice-versa. This would also confuse many users. We could recreate this screen determining reach-ability with as service such as ping.