removing dom element id "content", fixes #713 (#714)
removing dom element id "content", fixes #713 (#714)

* renaming dom element id "content" to "uv-content", fixes #713

* removing id="content" from content div, fixes #713
britishlibrary/UniversalViewer,britishlibrary/UniversalViewer,britishlibrary/UniversalViewer,britishlibrary/UniversalViewer,britishlibrary/UniversalViewer,britishlibrary/UniversalViewer