Add a dedicated Thumbnail item.

Allows thumbnail loading to be prioritized so items in the visible area
can be loaded ahead of those outside it and items with pre-generated
thumbnails ahead of those that need to be generated. Also includes
support for generating thumbnails from video using gstreamer.
Fix account test logic

Test account for sink property before testing transmission.
Encode the equivalences between stored values

I am not certain where these values are actually determined,
but better encoded than in comments.
Don't retrieve full message to extract account ID

Account ID is stored in the metadata record.
Remove duplicated code
Only load message metadata if possible

It is generally much slower to load the full message than just the
metadata; avoid this wherever possible.
Prefer the part location strategies provided by QMailMessage

The library functions traverse the message structure correctly to handle
unusual compositions correctly.
Remove code previously commented out

No reason to keep this code in the source.
Add a fillMode property to Thumbnail.
Merge pull request #29 from matthewvogt/improvements

Various simple improvements to the email-related classes
Added support for saving addresses and their types in SeasidePerson.
Move the gstreamer video thumbnailer into a separate binary.

Prevents linking against gstreamer until needed.
Merge pull request #30 from kypeli/master

Add support for address type saving in SeasidePerson.
Expose a method to get the total contact count.
Changed as per comment.
Merge pull request #31 from kypeli/master

Expose a method to get the total contact count from the model.
Remove remaining uses of gstreamer from thumbnailer plugin.

And warn in the video thumbnailer binary can't be built or loaded.
Merge pull request #28 from adenexter/thumbnail

Add a dedicated Thumbnail item.
Add 'count' property to SeasideProxyModel.

'count' will tell you the number of items in the currently filtered model.
Merge pull request #32 from kypeli/master

Add 'count' property that will tell the number of items the filtered model has.