Update cmake files to build against gstreamer-1.0
Fix GST_WRAPPER for GstTagList

GstTagList is now an opaque mini-object instead of a GstStructure,
so the WRAPPER macro needed updating.
Several specific getter/setters were replaced with g_value_*_boxed.

Update the function calls and hopefully get the reinterpret casts
for extracting the boxed values correct.
gst_structure_empty_new was renamed to gst_structure_new_empty
gst_caps_new_simple now requires a sentinal NULL for the varargs
gst_caps_do_simplify was renamed to gst_caps_simplify
gst_caps_union was removed, recommended replacement with gst_caps_merge.

gst_caps_merge takes ownership of the arguments so I removed the
const modifier.