support for Observer Widgets that are aware of underlying node types

```
Allowing Observer Widgets to know about the underlying node types would allow
for higher-level constructs, such as:

Observer Widget Name: interfaces
Observer Widget Command: ifconfig (for LxcNodes), brctl show (for LxBrNets)

or:
Observer Widget Name: packet counts
Would display packet count statistics for nodes, WLANs, EMANE WLANs, bridges,
etc.

```

Original issue reported on code.google.com by `ahrenh...@gmail.com` on 4 Aug 2014 at 4:29

Start by locating the Observer Widget implementation and the code that represents node types; no files or tests are named in the issue. Determine how widgets select commands for LxcNodes and LxBrNets and how packet statistics could cover nodes, WLANs, EMANE WLANs, and bridges. Done means the supported widgets can distinguish the relevant underlying types and present the requested information.

Written by the indexing model from the issue text.