[Tracker] Review request: tracker-sparql-qt

[Adrien Bustany <abustany gnome org>]

Hello there,

I would like to merge the tracker-sparql-qt branch into master. This
branch adds a new (optional) lib, libtracker-sparql-qt, which is a
simple wrapper around the libtracker-sparql synchronous API.
QT apps that want a low-level Tracker access for performance reasons
are better off with this library, rather than using higher level APIs.

The code itself is pretty stupid, I also added some minimal tests (I
will add more when I know if we can expect a running tracker at test
time) and a simple example program similar to tracker-sparql.

I expect the maintenance work for this lib to be minimal, and engage
myself to fix bugs for this lib.

Wrapping the async API is not planned yet, but might come one day.

The API/ABI stability guarantees should be the same as for
libtracker-sparql, however there might be an ABI breakage if we switch
some objects to QObject when binding the async API.

Cheers

Adrien