Make commandline interface available from the xfpanel-switch

[Shuhao]

First off let me just applaud you for this work. I needed this for a long time but it didn't exists, so I had to hack around with xfce4-panel.xml and such.

My request is not difficult, although some refactoring may be required after looking at the code. The idea is to expose the `load` and `save` command from panelconfig.py in the xfpanel-switch executable. This would avoid the ugly looking expression of:

python3 /usr/share/xfpanel-switch/xfpanel-switch/panelconfig.py load /path/to/config.tar.bz2

Also it brings more certainty that the command line load/save feature is supported.

[Marius Ghita (marius.ghita)]

I would also like this feature supported by default, for the moment I'll resort to the workaround @Shuhao shared (thanks for that).

[Gergő (pinter-gergo)]

I would also like this feature. I would like to switch panel configs from script.
Thanks

[Sean Davis (bluesabre)]

Change applied with this revision: https://bazaar.launchpad.net/~xfpanel-switch-dev/xfpanel-switch/trunk/revision/109