[conf.xml][GUI] GUI for selecting the desired active list of airframes.
[conf.xml] update configure gui

replace os.systems calls with generic remove and copy commands that work on multiple platforms.
The os.symlink still only works on posix systems of course.
[conf.xml] configure gui improvements

- sort list
- use python tools to get info about current conf, i.e. link to which file
[conf.xml] gui: exclude backups from list
[conf.xml] gui improvements

- non-editable combo box
- set current conf as active selection
- only ignore conf.xml if it's already a symlink
[conf.xml] gui: checkbox for showing backups
[conf] rename configre.py to select_conf.py

some other minor improvements
[conf] rename from *.xml.example to *_example.xml

- select_conf: personal conf file is conf_personal.xml
Merge pull request #536 from paparazzi/configure

[conf.xml][GUI] GUI for selecting the desired active list of airframes.