Skeleton code for a non-blocking UI thread for downloading dives from the DC

This is the skeleton code for a non-blocking ui-thread
It already creates the first-thread ( 'do not block the ui' )
and the second thread ('download from the dive computer')
We can in the future merge both in the same place - I didn't
want to do that now because the download function is written
in the libdivecomputer.c code, and I cant just transform that
to a QThread and use signals, so I used two threads for that.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>
Added code to cancel the thread.

I think it's self explanatory - When user clicks on
'Cancel', the interface will wait for the trhead to quit
then will close itself.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>
Populate the Vendor && Dive computer information.

This uses the QStringListModel to populate the items
of the QComboBoxes. I used a QHash to hold every Computer
of a particular Vendor. so, products[vendor] gives me
the full list of products from each vendor.

Signed-off-by: Tomaz Canabrava <tcanabrava@kde.org>
Implement rudimentary divecomputer download

Small changes to the names of elements the divecomputer download UI and
very simplistic first stab at populating the device_data_t structure.

This is lacking lots of things
- it should remember the last vendor / product used
- it should figure out which device (mount point) to offer
- it needs proper error handling

But it's a step in the right direction.

Signed-off-by: Dirk Hohndel <dirk@hohndel.org>