Import some of the files from Select2 3.5.0 Javascript system.

RhodeCode 2.2.5 used a version of Select2. Herein, we bring into
Kallithea only a few files directly from Select2 3.5.0 (6ef7155) upstream,
using the commands indicated below:

(cd /tmp; \
git clone https://github.com/ivaynberg/select2.git; \
cd select2; \
git checkout 3.5.0 \
)
mkdir rhodecode/public/js/select2
cp -pa /tmp/select2/select2.{js,css,png} rhodecode/public/js/select2/
cp -pa /tmp/select2/select2x2.png rhodecode/public/js/select2/
cp -pa /tmp/select2/select2-spinner.gif rhodecode/public/js/select2/
hg add rhodecode/public/js/select2/