Get rid of usrz/bootstrap-languages dependency

[php-coder]

Right now we're using usrz/bootstrap-languages from http://rawgit.com but we need to have it as a WebJar (especially as classic webjar, see webjars/webjars#1185).

Tech debt for e567018 (#216)

[php-coder]

Because of using external service, integration tests fail when they're running offline.

[php-coder]

Now I have a better idea -- don't use it at all :) We need only 2 tiny images with country flags and that's all. We can even embed these images in the page sources and don't load 2 external files (css/image).

[php-coder]

It turned out that loading of the https://cdn.rawgit.com/usrz/bootstrap-languages/3ac2a3d2b27ac43a471cd99e79d378a03b2c6b5f/languages.png leads to a redirect to
https://raw.githubusercontent.com/usrz/bootstrap-languages/3ac2a3d2b27ac43a471cd99e79d378a03b2c6b5f/languages.png