lua-factory: Load resources when available for each script

When loading a script called "XXX.lua", we will try to load an
"XXX.gresource" file from the same directory.

This allows lua sources to have icons, addressed through resource:///

https://bugzilla.gnome.org/show_bug.cgi?id=725147
lua-factory: Add support for boolean media properties

Such as "title-from-filename".

https://bugzilla.gnome.org/show_bug.cgi?id=740928
lua-factory: Add htmlentity files from GtkHTML

https://bugzilla.gnome.org/show_bug.cgi?id=729680
lua-factory: Use HTML entities helper

Which now supports more entities than what we supported.

https://bugzilla.gnome.org/show_bug.cgi?id=729680