Embed GEO label into metadata view for 2.8.x

This feature was developed as part of the 2.10.x-dev branch (69b046ceffcacb8ed81e7e34b96a6e3ffac3d5f4, 54bcaf7cd2b601dbd7a4787fb46d26c81a843915, 181b95fec3101749ac5b2d40b7a7d09d937ecb64) to embed GEO labels into the metadata view for GVQ documents.

The XHR to call the GEO label API is to a proxy script that allows cross-origin resource sharing (GeoViQua/geoviqua-tutorial#2)