[packagekit] Free and non-free filter

[Richard Hughes]

For the soon to be discussed EULA licence stuff, I want to add another
filter; "free" and "~free" based on the package licence.

For example, I could do "SearchDescription available;free
virtualisation" to get all the packages I could install for
non-proprietary solutions. I guess we can just whitelist the GPL, GPLv2,
GPLv2+ type strings for this and keep it nicely simple.

Of course, "free" can take all the usually debates on it's meaning, but
I take "free" to mean "FSF declared this licence as free" rather than
"this costs nothing".

The GPLv2+ matching should probably be shared somewhere in a nice
boolean=pk_backend_license_is_free(string) matching function. We can use
http://fedoraproject.org/wiki/Licensing as an initial reference, as I
guess most of the other backends will have similar short names.

So, I guess this feature is useful (it's useful to me, just so I install
the correct free flash package). I'm guessing it's mostly trivial to get
this information from the metadata, and so wouldn't be too hard to add.
Correct me if I'm wrong. Comments?

Thanks.

Richard.