create example presets

[boyska]

Examples are (sometimes) better than documentation itself.
Creating some preset may be nice both to have documentation on how to create them and to put them in a distro package (see #229 ) in something like /usr/share/libreant/examples.

Since people are lazy, providing examples also makes it more likely that field name will be more compatibile between different installations.

[ael-code]

At the moment we have just one example preset.

[boyska]

Yes, this issue aims at:

1. creating more presets (photo, leaflet, movie)
2. improve the existing ones
3. install them somewhere

I want to ship them with the debian package; some in /usr/share/libreant/examples, and some directly in /etc/libreant/presets/ so that they are enabled by default.