update EMANE support to allow XML editing and pre-existing XML files

```
Feature request to:
1. generate the EMANE XML during edit mode, allow user to edit, prior to running
2. allow user to specify pre-existing EMANE XML files
3. provide for variable substitution in pre-existing files (e.g. node 1
interface 2)
4. allow user to edit the full EMANE command-line
5. save/load subset of EMANE configurations values as presets (e.g. 802.11g
24M; RF-PIPE 450ms SATCOM)

```

Original issue reported on code.google.com by `ahrenh...@gmail.com` on 16 May 2013 at 5:25