Unicode support for search, length and STRING[] accesses (+ a fix for 3rd Party CGAL lib issue on Ubunti)

Support for using unicode strings in .scad files - e.g. 

    str = "Ленивый рыжий кот";
    character0 = str[0]; //Л
    len = length("Ленивый рыжий кот");
    search_res = search("Л","Лwithsinglecharstoo");


* Add GLIB (to build for test and normal build -- both with installed and built locally development files).
* Add to check dependencies.
* Update documentation.
* Add support for unicode chars to length and search builtin functions and [] for strings.
* Added unicode testing functions (length/[] access and search).
* Add GLIB to library info page in GUI.
* Fix a minor comment issue above search()

After @t-paul delivers his text() module then this will allow for the use of iteration over unicode chars and mean that those text functions can be used to write character at a time on objects such as spheres, cylinders, cubes (see https://github.com/brodykenrick/text_on_OpenSCAD for examples using this).