Add SVG logos for sixteen Wikisource wikis

This patch adds sixteen PNG thumbnails of SVG logos
drawn by Google Code-In students for the following
Wikisource projects:

* azwikisource (Azerbaijani);
* bgwikisource (Bulgarian);
* bswikisource (Bosnian — newly localised!);
* fiwikisource (Finnish);
* htwikisource (Haitian Creole — newly localised!);
* huwikisource (Hungarian);
* hywikisource (Georgian);
* iswikisource (Icelandic);
* lawikisource (Latin);
* liwikisource (Limburgish — newly localised!);
* ltwikisource (Latvian — newly localised!);
* mkwikisource (Macedonian);
* slwikisource (Slovene);
* srwikisource (Serbian);
* thwikisource (Thai);
* trwikisource (Turkish).

No community consensus was sought since the logos are
as close to 1:1 replicas as possible; see bug for
more information on that.

I decided /not to/ submit new logos for the Bengali,
Catalan, Greek, Esperanto and Estonian Wikisource
projects, as they still require some work; I might
do that next time.

The logos are already protected on Commons against
re-uploads and name changes; I've done that myself.

Attribution notice:

All logos are (c) by the Wikimedia Foundation.

* Azerbaijani, Bosnian, Finnish, Haitian Creole,
Hungarian, Icelandic, Latin, Limburgish, Latvian,
Macedonian, Slovene, Serbian and Turkish Wikisource
logos created by Thomas Lam;
* Bulgarian and Thai Wikisource logo created by
Idofen;
* Georgian Wikisource logo by Natasha Murashkina.

Bug: 52019
Change-Id: Ie13fd9ca607cf0cba5154004297afbbdbad032dd